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PUB3 . 


Laemmle Donation 




II 'I 

A Guide for 




Published by 

Pullman Building, 17 Madison Avenue 

Copyright, 1910 


Entered at Stationers' Hall, 
London, England. 

Copyright in the United States, 1912; 

Copyright in Great Britain, 1912; 

Copyright in Canada, 1912, 



New York. 

Copyright in the United States, 1916; 

Copyright in Great Britain, 1916; 

Copyright in Canada, 1916, 


New York. 
All Rights Reserved. 

Index to Contents 


Aberration, Chromatic 94, 98, 124 

Aberration, Spherical 94, 97, 123 

A. C. Action How to Trace It 16 

A. C. and D. C, Difference Between 13 

A. C and D. C., Relative Efficiency of 290, 294 

A. C. or D. C, to Find Out 667 

A. C Wires Must Be in Same Conduit 240 

Adjusting Intermittent Sprocket 461 

Adjusting the Tension Springs 463 

Airdomes 669 

Airdome Site, Selecting. . . . . 672 

Alternating Current, Definition of 22 

Alternating Current, How Generated 8 

American Standard Projector, Instructions for 566 

Ammeter and Voltmeter for Operating Room 235, 248 

Amperage 157 

Amperage, Economic Limit of 292 


Definition of 19 

Hour, Definition of 19 

Term, Definition of 23 

What the Term Means 26 

Anchoring the Machine 236 

Aperture Plate Tracks Worn 465 

Aperture, Standard Size 476 


Calculating Its Candle Power 293 

Comparison of Candle Power 293 

Comparison of Candle Power from Mercury Arc 

Rectifier and Through Rheostat. 294 

Controller 303 

Lamp, The 268 

Position of Crater of 295 

Stream 291 

Voltage 31, 301, 323 

Architect's Plans, Checking of 668 

Asbestos Wire Lamp Leads 50, 233, 271, 313 

Back Focus, Definition of 92 

Back Focus, How Found 104 

Back Focus, Why Important 122 

Baird Projector, Instructions for 546 

Batteries, Renewal of 649 




Calculations, Electrical 28 

Candle Power of Arc 293 

Capacity, Wire, Table of 42 

Capacity, Wire, Figuring Voltage Drop 45 


Arc Stream 291 

Calculating Candle Power of Crater 293 

Care of 289 

Chemicalizing 288 

Economizers 302 

Fresh Carbons in Lamp, Effect of 301 

Hard and Soft 287 

Hard Spots 287 

How Made 284 

Inspect When Buying 287 

Mushroom Cap on Lower 299 

Resistance They Offer 288 

Set, Best Results 301 

Set for A. C 297 

Setting 290 

Side Lining 300 

Size of 285, 287 

Solid vs. Cored Lower 286 

Stubs 287 

Why D. C. Crater Is Larger Than A. C 290 

Carpeting 647 

Chair, Operator's 235, 245 

Chalk Surface for Screens 189 

Cheap Equipment 667 

Choke Coil 344 

Choke Coil, Preddy Economizer 363 

Chromatic Aberration 94, 98, 124 

Chromatic Aberration of Condenser Beam 124 

Cleaning Carbon Clamps, Importance of 270 

Cleaning Film 206 

Cleaning Lenses 108 

Cleaning Machine After Film Fire 208 

Closets for Operator 231 

Coating for Screens 183 

Coefficient, Temperature 39 

Coloring Incandescent Lamps 668 

Commutator, Care of 372 

Commutator, Definition of 21 

Compensarcs, A. C 353 

Compensarc, A. C, Rules for Operation 355 

Condenser Holder 266 

Condenser Holders, Freddy, Elbert 267 

Condenser Lenses, Distance from Film 131 

Condenser Lenses, Selecting 128 

Conductor, Definition of 22 

Conductors, To Find Area of 48 




Conductors, Properties of 40 

Conduit for Wires 212, 240 

Conjugate Foci, Definition of 91 

Conjugate Foci, Explanation of 95 

Connections, Series and Multiple . 330 

Connecting to Two Sources of Supply 252 

Cost of Light from A. C. Through Transformer and D. C. 

Through Rheostat 294 

Coulomb, Definition of 19 

Crater, Position of 295 

Cycle, Definition of 22 

Diameter of Objective Lens 110 

Difference Between A. C. and D. C 13 

Dimmer, Definition of 22 

Direct Current, Definition of 22 

Direct Current, How Generated 11 

Dissolving Moving Picture 606 

Dissolving Shutter 605 

Dissolving Stereopticon 603 

Distance Condenser to Film 131 

Door of Operating Room 213 

Double Sets of Fuses 86, 252 

Double Spot, One Reason for 297 

Double Throw Connection for Projector 250 

Dynamo, Principle of Operation 11 

Edison, Model D, Instructions for 579 

Economizer, Hallberg A. C 360 

Edison Economy Transformer 356 

Edison Super-Kinetoscope 477 

Efficiency, How Calculated 23 

Efficiency of A. C. and D. C 290, 294 

Electric Conductors, Properties of 40 

Electric Meters 655 

Electrical Terms 18 

Electrical Terms, Explanation of 24 

Electricity, How Generated 5 

Electro Magnetic Field, Definition of 22 

Electro Motive Force, Definition of 22 

Emergency Announcement Slides 239 

Emergency Light Circuit, Fusing 86 

Employes 661 

Emulsion Deposit on Tension Springs 464 

End Play in Intermittent Sprocket 462 

Equipment Operating Room 231 

Equivalent Focus, Definition of 93 

Equivalent Focus, How Measured 104, 108 

Exit Lights: 640 

Eye Strain 153, 175, 472 

I 7 easter Non-Rewind Machine 318 

Figuring Seating Capacity 643 



Film. PAGE 

Cement Formulas 197 

Cleaner, Mortimer 206 

Cleaner, Ideal 207 

Cleaning 206 

Containers 596 

Description of 192 

Inspection of 201 

Leader and Tailpiece 199 

Life of 208 

Measuring 210 

Mending 195 

Moistening When Dry 204 

Notching Pliers 203 

Perforations 194 

Stretched 204 

Thickness of 194 

Where to Keep 203 

Fire-proofing Solution 189 

Fire Shutters for Ports 222 

Floor of Operating Room 214 

Floor, Slope of Auditorium 640 

Focus, In and Out, Cause of 466 

Foot-pounds, Definition of 19 

Formostat, The 365 

Fort Wayne A. C. to D. C. and D. C. to D. C. Compensarcs. 382 

Fuses 76 

Cartridge 79 

Copper 83 

Emergency System 86 

In Case of Trouble 84 

Link 80 

Plug 80 

Projection Circuit 81 

Table of Sizes 82 

Where Installed 85 

Fusing for Motor Generator 82 


Cap on Lower Carbon 299 

Definition of 22 

For Lamp 268 

Where Obtained 269 

Generator, Electric 11 

Glass in Ports 230 

Ground, Establishing Permanent 259 

Ground, Testing Rheostats for 260 

Grounding Machine, Reason for 262 

Grounds 255 

Grounds, Definition of 22 

Hallberg's D. C. to D. C. Economizer 415 

Hallberg's Twentieth Century Motor Generator 419 




Haze on Screen, Reason for 168 

Heating 632 

Heating and Ventilating 624 

Height of Screen Above Floor 181 

High-Class Projection, Importance of 151 

High-Grade Lenses 110 

Horse Power, Definition of 20 

Inclosed Switches 64 

Induction, Definition of 23 

Inductor, Power's 359 

Inductor, Power's, Size and Weight 360 

Insulation . . 50 

Definition of 23 

Rubber Covered 51 

Testing 52 

Weather-proof 53 

Intermittent Sprocket, Used Too Long. 233, 462 

Keystone Effect 154 

Keystone Effect, Eliminating 156, 468 

Killowatt-Hour, Definition of 20 

Lamp, The 268 

Angle of 273 

Insulation 272 

Lubrication of 268 

Necessary Adjustments 273 

Lamps, Compared 270-1-2 

Lamphouse, The 262 

Arc Projector 265 

Condenser Holder 266 

Keeping Clean 265 

Lighting Interior 302 

Ventilation 262 

Ventilation, Best Method 263 

Ventilation, Effect of Lack of 263 

Leaders for Films 199 

Lens System, Matching 113 

Lens Tables of Small Value 105 

Lenses 91 

Altering Distance Between Factors 101 

Cleaning 108 

Cleaning the Objective 109 

Diameter of Condensing 128 

Diameter of Objective 110, 122 

Dirty, Loss of Light 102 

Explanation of Focus 95, 101 

Figuring Sizes 105 

High Grade 110 

How Designed 96 

Improving Definition 102 

Loss of Light in 159 



Lenses (Continued). PAGE 

Measuring 103 

Measuring E. F. Accurately 108 

Selecting Condenser Lenses 128 

Spread of Light Ray 102 

Table for Matching 141 

License Law, Draft of 621 

License, Operator's 617 

Life of Film 208 

Lighting the Auditorium 633 

Limelight Projection 674 

Limit of Amperage 292 

Lining Cam and Sprocket Shafts 466 

Lining the Optical System 112 

Lining the Sprockets 460 

Location of Operating Room Ports 215 

Loss Through Resistance 41, 334 

Lugs, Wire Terminal 87, 88 

Magnetic Field, Definition of 22 

Martin Rotary Converter 405 

Matching Up Lens System 113 

Measuring Film 210 

Measuring Lenses 104 

Measuring Wires 48 

Mechanism, The (See "Projector") 457 

Mechanism, The, General Instructions 457 

Meter, Reading 657 

Mill-foot Standard of Resistance 42 

Minusa Screen 187 

Mirror Screen 185 

Mirroroid Screen 187 

Mortimer Film Cleaner 206 

Moistening Dry Film 204 

Motiograph, Instructions for 528 

Motor Drive. 

Do Not Belt to Fly Wheel 277 

Elbert 275 

Home-made 279 

Multiple Clutch 277 

Preddy ' 276 

Wallstad Projection Stand 280 

Spring Switch 274 

Motor Driven Machines 273 

Motor Generator. 

Ammeter and Voltmeter 372 

Bearings Run Hot. . . '. 381 

Care of Commutator 372 

Fort Wayne 382 

General Instructions 368 

Hallberg's D. C to D. C. Economizer 415 

Hallberg's Twentieth Century 419 



Motor Generator (Continued). PAGE 

Heating 381 

Locating Installation 368 

Martin Rotary Converter 405 

Oil 371 

Sparking 374 

Wagner Rotary Converter 407 

Wotton Rexolux 395 

Multiple Arc System 55 

Musicians 663 

Musicians, Light for 634 

Objective Lens, Cleaning 108 

Objective Lens, Description of 99 

Objective Lens, Test for Distortion 100 

Ohm, Definition of 20 

Ohm, Explanation of 27 

Oil for Projector 457 

Operating Room 210 

Door 213 

Equipment 231 

Film Storage 596 

Floor 214 

Model Installations : 244-6-7-8-9 

Observation Port 219 

Ports 215 

Size of Feed Wires 239 

Supplies 232, 234 

Toilet Conveniences 232 

Vent Flue 227 

Ventilation 228 

Wiring 239 

Operator Remaining at Machine 235, 279 

Operator's License 617 

Operator's Report 623 

Operator's Tool Kit 237 

Optical Axis, Definition of 91 

Optical System, Lining Up of 112 

Outlining Screen with Black 178 

Overspeeding 151 

Persistence of Vision 472 

Polarity 5 

Changer 252 

Definition of 21 

Explanation of 24 


For Operating Room 215 

Glass in [ 230 

Observation , 7j9 

Shutters for ' 222 




Power's 6B, Instructions for 491 

Preddy Economizer 363 

Projection 147 

By Limelight 674 

No Excuse for Shadows 149 

Overspeeding 151 

Projector, The 262 

Adjusting Intermittent 461 

Adjusting Sprocket Idlers 466 

Adjusting Top Gate Idler 462 

American Standard, Instructions for 566 

Baird, Instructions 546 

Edison, Model D, Instructions 579 

Edison Super-Kinetoscope 477 

Eliminating Keystone Effect 469 

Emulsion Deposit on Tension Springs 464 

End Play in Intermittent Sprocket 462 

Extra Framing Carriage 462 

Handling Small Screws 476 

In and Out of Focus, Cause 466 

Lining Magazines of 467 

Lining the Sprockets 460 

Lining Sprocket and Cam Shafts 466 

Motiograph 528 

Oil for 457 

Power's 6B 491 

Reels for Operating Room 467 

Revolving Shutter 469 

Shutter and A. C 473 

Standard Aperture Size 476 

Take Up 592 

Take-Up Adjustment 459 

Tension, Adjustment of 463 

Threading the Machine 594 

Upper Magazine Tension 468 

Worn Aperture Plate Tracks 465 

Worn Sprocket Teeth 462 

Properties of Conductors 40 

Properties of Resistance Metals 40 

Radium Gold Fibre Screen 188 


Comparative Results 432 

General Electric 434 

Installation 431 

Light in Operating Room Objectionable 432 

Mercury Arc 428 

Trouble Chart 433 

Tube, Operating Principle 429 

Westinghouse 446 

Reflection, Regular and Diffuse 168 

Refraction, Definition of 92 




Relative Efficiency A. C. and D. C 291, 294 

Report, Operator's 623 

Resistance 34 

As Applied to Projection Circuit 322 

Circuits, of, Figuring It 44 

Copper Wire, of 43 

Definition of 21 

Devices 337 

Different Metals, of 38 

How It Acts 34 

Loss Through 41, 334 

Materials, Properties of 40 

Metals, Properties of 40 


A. C. and D. C 333 

Adding Extra Resistance 327 

Adjustable, How It Works 324 

Amount of Heat Permissible 329 

Coil, How to Make 327 

Coils vs. Grids 329, 330 

Examining Connections 328 

Extremely Wasteful 333 

Fan Blowing On 328 

Figuring Connections 335 

Fixed Resistance of Adjustable 325 

Home Made of Iron Wire 329 

How to Reduce Noise When Using Them on A. C. 333 

Inductive Effect of A. C 333 

Locate It Outside of Operating Room 328 

Location of 227 

Near Ceiling and Vent Flue 328 

Resistance Rises with Age 336 

Temporary Repair 326 

Use on A. C. Bad Practice 333 

Use Grid Type on A. C 333 

What Happens if Spirals of Coils Touch 337 

What They Do 322 

Wire Coil, What They Are. 337 

Why Noisy on A. C 333 

Rule of Thumb 32 

Screen, The 166 

Areas 165 

Chalk Surface 189 

Character of Surface 169 

Coatings 183 

Distribution of Light 170 

Eye Strain 175 

Fire-proofing 189 

Flat Surface 177 

Height Above Floor 181 

Illumination, D. C. and A. C 291 



Screen (Continued). PAGE 

Illumination Percentages 164 

Interfering Light 169 

Locating at Front of House 180 

Metalized Surface 172 

Minusa Gold Fibre 187 

Mirror 173, 185 

Mirroroid 186 

Outlining the Picture 178 

Putting on the Cloth 191 

Radium Gold Fibre 188 

Reason for Haze 168 

Reflection of Light 168 

Simpson Solar 186 

Size of Picture 181 

Stippled Surface 189 

Stretching Its Surface 190 

Table of Areas 165 

Tinted Surfaces 178 

Transparent 174 

Where Vaudeville Is Used 181 

White Wall or Sheet 171 

Seating 642 

Seating, Figuring Capacity 643 

Seating, Loge Seats 643 

Series and Multiple Connections 330 

Setting the Carbons 290 

Short Circuit, Definition of 21 

Shunt Circuit, Definition of 21 


Distance from Lens 474 

Inside and Outside 475 

Revolving, Principle of 469 

Three and Two Wing and A. C 473 

Side View, Effect of 154 

Simplex Mechanism, Instructions for 513 

Simpson Solar Screen 186 

Size of Picture 181 

Slide Coatings 615 


Coloring 614 

Emergency 239 

Handling Them 612 

Making Them 612 

Stereopticon 609 

Slope of Auditorium Floor 640 

Soldering Fluid 90 

Spherical Aberration 94 

Splices, Wire 89 

Spotlight, The 598 


Sprocket. PAGE 

Adjusting Intermittent 461 

End Play in Intermittent 462 

Idlers, Adjusting 466 

Teeth, Worn 462 

Static Electricity, Definition of 22 

Stereopticon, The 600 

Coloring Slides 614 

Dissolving Shutter 605 

Handling the Slides 609 

Making Slides 612 

Slides 609 

The Dissolver 603 

Street Mains, Definition of 22 

Supplies for Operating Room 232, 234 

Switchboards 67 

Switchboards, Exit and Emergency 72 

Switchboards, Stage 73 

Switches 63 

Care of 66 

Inclosed 64 

Metal Cabinet for 67 

Proper Location of 64 

Use of Various Types 65 

Synchronism, Definition of 24 


Carbon Sizes 287 

Experiments with Arc 301 

Millimeter Equivalents 289 

Screen Areas 165 

Screen Illumination Percentages 164 

Small Wire Diameters 314 

Stereo Lenses 107 

To Match Lenses 141 

Wire Capacities 42 

Take-Up Adjustment 459 

Take-Up, Faults of Old Style 592 

Temperature Coefficient 39 

Temporary Show, Connecting Up for 664 

Tension Spring, Adjusting 463 

Terminals, Wire .....87, 88 

Terms, Electrical, Definitions 18 

Terms, Electrical, Explanation of 24 

Test Lamp for Grounds 257 

Testing Insulation 52 

Testing Objective Lens for Distortion 100 

Testing Rheostat for Ground 260 

Testing Voltage 666 

Threading the Machine 594 

Three-Phase Current 17 




Three-Wire System 56 

Three- Wire System, Connecting Arcs 242 

Toilet Conveniences for Operating Room 232 

Toledo Non-Rewind 315 

Tools in Order 238 

Tool Kit for Operator 237 

Torque, Definition of 23 

Transformer, The , . 343 

Action of 345 

Auto 346 

Compensarcs 353 

Construction of 343 

Definition of 23 

Edison Economy 356 

Fusing 351 

Hallberg A. C. Economizer 360 

How Amperage Is Changed 349 

Power's Inductor 359 

Primary vs. Secondary Terms 344, 349 

The Formostat 365 

Theory It Utilizes 345 

Wiring of Compensarc 354 

Two-Phase Current 18 

Two-Wire System 

Use of Electrical Terms in Calculations 28 

Vent Flue for Operating Room 227 

Ventilation and Heating 624 

Ventilation for Operating Room 228 

Ventilation, Winter 633 

Volt-Coulomb, Definition of 19 

Volt, Definition of 20 

Voltage Drop, Figuring It 45 

Voltage, Explanation of 25 

Warning, A 668 

Watt, Definition of 20 

Watt, Explanation of Term 27 

Watt-Hour, Definition of 20 

Watt Meter, Definition of 23 

Weather-proof Insulation 53 


Capacity, Figuring Voltage Drop 45 

Capacity, Table of 42 

Gauges 49 

Measuring 48 

Splices 89 

Systems 54 

Terminals '. 87, 88 

Wiring the Operating Room 239 

Worn Machine Parts, Do not Use Them 233 

Worn Sprocket Teeth 233, 462 

Wotton Vertical Rexolux. 395 


Acknowledgement Is Hereby Made 


Attleboro, Mass., 

For the Drawings for a Large 

Number of the Cuts in 

This Handbook. 


Author's Note 


THIS book is dedicated to the motion picture operator as 
a token of appreciation of the important part he plays 
in the presentation of the photoplay. That it may be 
helpful in hastening the day of perfect motion picture pro- 
jection is the desire of the writer, and he trusts that a careful 
perusal of its pages may stir the ambition and increase the 
ability of every reader. 

October, 1910. 

Publishers Note 


THE remarkable vogue of the motion picture and the 
rapid strides it has made in public favor as an enter- 
tainment and educational factor have had their draw- 
backs. Chief among these has been the impossibility of 
securing a sufficient number of men with the necessary 
knowledge and experience to fill important positions. 

THE MOVING PICTURE WORLD has, in no small measure, con- 
tributed to the success of the picture, and the articles in this 
book were written to give helpful information in regard to 
the many problems that may arise in connection with the 
duties of the manager and operator. With a few exceptions, 
the articles have already appeared in THE MOVING PICTURE 
WORLD, but they have been revised and amplified and are 
herewith presented in compact form to comply with popular 

Mr. Richardson has avoided technical terms, and his plain 
language and matter-of-fact style bespeak for this book the 
same degree of popularity which attaches to the Operators' 
Column which he still conducts in the pages of 

October, 1910. 

Author's Note 


LIKE the former edition, this book is dedicated to the 
moving picture operator, upon whose skill in the pro- 
jection of the magnificent work of our modern pro- 
ducers so very much depends. Since the inception of the 
Projection Department of THE MOVING PICTURE WORLD and 
the publication of the first book rapid strides have been 
made in the perfection of projection. The author hopes and 
believes that this work will serve to even further advance and 
perfect projection to the end that the photoplay may become 
still more firmly fixed in the affections of the amusement- 
loving public. 

October 30, 1912. 

Publisher's Note 


THE enormous increase in popularity of the motion 
picture during the 'past few years in all countries is 
one of the marvels of the day. The moving picture 
is now far in advance of all other forms of public entertain- 
ment among all classes and draws a daily patronage that is 
beyond belief. 

In no other country, however, do the pictures have quite as 
good a hold on the public favor as in the United States. This 
is in great measure due to the enterprise and higher ideals of 
the film manufacturers in this country. It is also due in great 
measure to the care and attention given to programs, theater 
management and especially the projection of the pictures by 
the exhibitors throughout the United States and Canada. 

The first edition of this work was published over two years 
since and has been of immense value and help to operators 
throughout the country. This edition has been greatly en- 
larged and will be found much more complete in every way. 
It will undoubtedly remain the standard work in its field for 
many years and is a worthy monument to its author's ability 
and painstaking effort. 


November, 1912. 

Author's Note 


AS in the case of the first and second editions, I believe 
it is but right and proper that this, my latest effort, 
should be dedicated to the moving picture operator, 
upon whose shoulders rest, in large degree, the welfare of 
the entire moving picture industry. The author has faith to 
believe that this book will be favorably received by the 
fraternity and trusts it will accomplish a large amount of 
good for all students of projection. 

In order to do justice to the magnificent productions of 
today it is necessary that the moving picture operator have 
a wide range of knowledge and that he be capable of apply- 
ing that knowledge in the best possible way. The day of 
guesswork in projection is past. The author feels that while 
this book will be of great aid to the moving picture operator, 
it will also indirectly be of equally great help to the pro- 
ducers and all others connected with the industry by reason 
of the fact that it is the finished product which is placed in 
the hands of the moving picture operator, who may either 
reproduce it on the screen as a magnificent spectacle or a 
shadowy, jumping travesty on the original. 

November, 1915. 

Publisher's Note 


THERE is little to add by the Publishers in introducing 
this new edition. The first and second editions of 
this work were most complete and instructive at 
the time of their publication. Each edition was an improve- 
ment over the previous one, and this book much more than 
either of its predecessors not only reflects the wonderful 
progress and improvement in moving picture projection but 
points the way to still greater advancement. 

The author has spent all of his time for many years in the 
study of projection, and we confidently believe this com- 
prehensive work will meet with the unqualified approval of 

December, 1915. 

Go to your work each day 
as though it were your 
first day on a new job 
and you had to make good. 


IN order to have a comprehensive understanding of elec- 
trical action it is essential that the operator have a very 
clear and thorough understanding as to precisely what 
polarity means, and how it acts, because the whole super- 
structure of electrical action rests thereon. 

The electric circuit with which the operator comes into con- 
tact consists of two wires no more and no less. There may 
appear to be more, as, for instance, in a three-wire system, 
but, as a matter of fact, so far as electrical action be con- 
cerned, every electric circuit is composed of two wires, viz.: 
the positive and the negative, and it is the affinity these two 
wires (which represent the poles of the dynamo) have for 
each other which constitutes "polarity." There always has 
been and still is controversy between eminent theoretical 
electricians as to the exact nature of the action which takes 
place as between the positive and the negative wire. To avoid 
all confusion, however, we will lay aside technical questions 
and accept the common statement that current seeks always 
to flow from the positive to the negative. Having accepted 
this as the fact it may be further said that the inclination of 
the current to escape from the positive to the negative is 
similar to the efforts of steam to escape from the boiler into 
the open air. When steam escapes from the boiler to the 
open air it loses its pressure in the process. When electrical 
energy escapes from the positive to the negative it does 
exactly the same thing, and that is why it seeks to escape; 
also that is why it will perform work in the process of escap- 
ing. The pressure in the boiler will force the steam to the 
open air through the cylinder of an engine, moving the piston 
and thus performing work in the process. The electric cur- 
rent will perform work in the motor or the lamp, since it can 
get from positive to negative by so doing and thus lose its 
pressure. This electrical affinity is termed "polarity," and its 
strength, which may be much or little, is measured in volts. 


And now let me make one point very clear. Electrical 
affinity or polarity only exists between the positive wire and 
the negative wire attached to the same dynamo or battery. 
There is absolutely no electrical affinity between the negative 
wire attached to one generator and the positive wire attached 
to another generator, unless the generators themselves are 
electrically coupled, as in the case of the three-wire system. 
You could set two generators running, side by side, each 
generating 500 volts, and touch the positive of one generator 
to the negative of the other machine without any effect what- 
ever, but the instant you touch the positive of either one 
to the negative of the same machine there will be fireworks. 

And now let us go a little further: The general idea is that 
current seeks to escape from the wires into the ground. 
This is not true except in so far as the ground may offer a path 
from positive to negative. If you could have a generator 
and wire system working at 5000 volts, or any other voltage, 
thoroughly and completely insulated (a condition never found 
in actual practice), you could stand with your bare feet on 
the wet ground and handle either wire of the circuit without 
any danger whatever, but the instant one of the .wires develops 
current carrying connection with the ground and you stand 
on the ground and touch the other wire you get a shock, by 
reason of the fact that the current, leaping through your body 
into the earth and following the earth to the location of the 
ground on the opposite side, makes escape into the negative. 
If you happen to be holding the negative wire, that makes 
no difference, except that instead of escaping into your hands 
and passing through your body into the earth the current 
escapes through the ground at the positive into the earth, 
follows the earth to your body and up through your body 
to the negative. 

In closing this topic let me repeat that the term polarity 
expresses the electrical difference between positive and 

How Electricity Is Generated 

MORE and more it is becoming essential that the mov- 
ing picture operator have a comprehensive knowledge 
of electrical action, not only as pertains directly to 
the projection arc circuit, but also as relates to dynamos and 
motors. An ever increasing number of moving picture thea- 
tres are installing either motor generator sets or mercury arc 
rectifiers for the changing of alternating current into direct 


current, or else isolated light plants consisting of a dynamo 
driven by a gas, gasoline, kerosene or steam engine. The 
operator is usually the man who is expected to take charge of 
and operate these isolated plants, and most certainly it is a 
part of his duties to handle and take care of a motor gener- 
ator set, or other device used for the rectifying of current. 
Therefore, I repeat, the up-to-date competent moving picture 
operator must have a very comprehensive knowledge of elec- 
trical action. 

This, the third edition of my Handbook, is, like former 
editions, a work for practical men. In this book I shall, as I 
have in the past editions, pay a great deal more attention to 
practical things than to fine-spun theories and strictly tech- 
nical correctness. 

We do not know the precise nature of the force we call 
electricity. We do not know what it consists of. Its com- 
ponent parts have never been analyzed. We only know 
that it is a mighty force, which apparently has neither sub- 
stance nor weight. It is a peculiar state, or condition, in and 
immediately surrounding a wire attached to a battery or 
generator which is not found in any wire not so attached. 

We do, however, know how to handle this mysterious force, 
and bend it to our will. In fact, our knowledge of electrical 
action has become so complete that the mighty giant is as a 
child in our hands. We have chained it to the wheels of 
progress, and it has become a slave to mankind. 

Electricity may be divided into three distinct classes, viz. : 
Static electricity, magnetism and electric current, meaning, 
by the latter, current which is generated by batteries or by 
an electric dynamo. 

If you take a glass jar, of any convenient size, fill it two- 
thirds full of water, and then put in ordinary sal amoniac in 
proportion of a pound to the gallon of water, and in this 
solution suspend a piece of ordinary sheet copper, of con- 
siderable dimensions, and near to it but not touching suspend 
a piece of zinc, also of considerable dimensions, you will have 
the simplest form of what is known as an "electric battery." 
Now if you join the copper to the zinc by means of a piece of 
copper wire, current will flow between the two, or, more cor- 
rectly speaking, from the copper to the zinc, the copper being 
positive and the zinc negative. A properly proportioned bat- 
tery of this sort will generate about one volt pressure, and 
will put forth a considerable amperage while it lasts. It would 
be theoretically possible to construct and connect together 



a sufficient number of batteries of this kind to operate a pro- 
jection arc lamp, but, though theoretically possible, it would 
nevertheless be highly impractical. In practice the use of the 
battery is largely confined to the ringing of bells and buzzers, 
the operation of telegraph instruments and similar light ser- 
vice where but comparatively little energy is required. 

Electric current used for ordinary light and power purposes 
is generated by what is known as a dynamo, or generator, the 

two terms being inter- 
changeable when used in 
this connection. The dynamo 
depends for its action upon 
magnetism, and the fact that : 
When an electric conduct- 
or is moved in an electric 
field a current of electricity 
is generated therein which 
will flow in a direction at 
right angles to the line of 

, . In Fig. 1 we see this law 

illustrated, N and S being the 

q north and south poles of an 

f V ordinary horseshoe magnet, 

the dotted lines representing 
magnetic "lines of force," 
which constantly flow between 
the poles of all electric mag- 
nets. The space occupied by 
these lines of force is termed 
a "magnetic field," and with 
a magnet of the type shown 
in Fig. 1 this field is, of course, strongest directly between the 

A represents an electric conductor, say an ordinary copper 
wire, with its ends joined by wire B, so that a continuous cir- 
cuit is formed. If this wire be moved upward, in the direc- 
tion of arrow A, an electric current will be generated therein, 
which will flow along the wire in the direction of arrow C, or 
at right angles to the line of motion. // the wires were moved 
downward through the magnetic field in the direction of arrow 
X, instead of up, the current in the wire would flow in the op- 
posite direction, as per dotted arrow Y, it, of course, being under- 
stood that the ends of the wire passing through the magnetic 
field must always be joined, so that a complete circuit is formed. 

Figure 1. 


No current would flow if the wire were merely a straight length, 
with its ends unjoined. 

Now let us take a step in advance and examine Fig. 2. Re- 
membering that if the electrical conductor in Fig. 1 be moved 
upward the current will flow to the right, and if it be moved 

downward it will flow to the 
left, transfer your gaze to 
Fig. 2, where you will see a 
loop of wire, X X, so ar- 
ranged that it may be rota- 
ted on a spindle. One end 
of this loop connects to ring 
A, and the other end to 
ring B, and the ends are 
joined by means of brushes 
C and D and the wire E 
(outside circuit) attached 
thereto. Now if we revolve 
this wire loop (armature) 
in the direction indicated 
by small crank arrow, 
the side next us will move 
upward, while the other 
moves downward, so that 
on the side of the loop next 
us the current will flow to 
the right, toward collecting 
ring B, whereas on the 
other side it will flow to 

Figure 2. 

NOTE. Strictly speaking it Is vol- 
tage (E.M.F.) which is generated, but 
my purpose is served by the use of 
the term "current," which is less 
confusing to the student. 

the left, away from the col- 
lecting ring A, but by reason of the fact that the wire is in the 
form of a loop the current flows clear around the coil, out 
through brush A, around wire E to brush B, and back into the 
loop again, and thus we have the electric action of a generator 
exemplified. This is how current is generated. 

But this is not all, since at the end of one-half revolution the 
two sides of the coils will have changed place, and the current, 
still moving in the same direction with relation to the magnet, 
will then be flowing away from ring A, and toward ring B, 
which, as you will readily see, means the reversal of the current 
within the wire coil itself, as well as in outside circuit B, and 
this reversal must, perforce, occur with every half revolution of 
the coil, or armature. In considering this matter, bear carefully 
in mind the fact that, with relation to the poles of the magnet, 
the current will always flow in the direction indicated by the 



arrows; also remember that this wire coil merely represents one 
coil out of the many wound upon the armature of a generator, 
but that the electrical action in all armature coils is essentially 
the same as that of the one described. 

I think after a careful study of the foregoing you will 
readily grasp the idea, and understand how current is gener- 
ated in an armature coil; also why the current in the armature 
of a dynamo constantly reverses its direction, or, in other 
words, is "alternating." 

The current in the armature of all generators reverses its 
direction as above set forth, though in multipolar dynamos 
(generators having more than two poles) it is reversed every 
time the coil passes from the influence of one set of poles 
into the influence of another set of poles, which may occur 
several times to each revolution of the armature. 

Figure 3. 


All this is just as true of direct current generators as it is of 
alternating current generators, but in the case of the direct 
current dynamo the alternating current generated in the 
armature itself is rectified by what is known as the "commu- 
tator," so that the current on the outside circuit flows constantly 
in one direction, or, in other words, is direct current. As a 
matter of fact all electric dynamos generate alternating cur- 
rent in their armatures. A study of what has gone before 
will show that this could not possibly be otherwise. 

Fig. 3 is an illustration of a simple form of dynamo, tech- 
nically known as a "two-pole, shunt-wound" machine. N is 
the north and b is the south pole of its "field magnet." The 
dotted lines between its pole pieces represent lines of magnetic 
force, and its voltage and capacity will depend upon (a) the 
number of lines of magnetic force passing between the two 
poles, or, in other words, the "strength of the magnetic field," 
or, in other words, the "density of the magnetic flux" per 
square inch of the surface of the pole pieces on the side next 
to the armature; (b) the number of coils of wire the armature 
contains, and, (c) the rotary speed of the armature. Of 
course, there are other details of construction, such as the 
kind of iron in the magnets, size of magnets, kind of arma- 
ture core, etc., which are of great importance, but these items 
only have to do with the efficiency of the machine, not its 
operating principle. 

The magnet of this type of machine is what is termed a 
"permanent magnet." That is to say, the iron of its magnets 
remains magnetized after the armature has come to rest. The 
slight magnetism retained by the iron after the armature has 
stopped is termed "residual magnetism," and it is this residual 
magnetism which enables the machine to start up without 
having its magnets excited from an outside source. The 
residual magnetism is, however, very weak, and, in practice, 
running at normal speed, the average dynamo would generate 
five or at the most ten volts when operating merely on the 
residual magnetism of its field magnet, which would be totally 
inadequate for commercial purposes. 

Now the voltage generated by the armature will depend 
upon the number of lines of magnetic force which the con- 
ductors upon that armature cut per second. The number of 
lines of force cut per second, and in consequence the voltage 
could, of course, be increased by increasing the number of 
coils on the armature, but in practice this would require an 
armature of huge proportions. The same effect could be had 
by increasing the speed of the armature, but there, too, is a 


limit, and high speeds are objectionable. It therefore follows 
that the really practical method of increasing the number of 
lines of force cut per second is to establish the speed of the 
armature and the number of coils thereon, and then increase 
the density of the magnetic field until the desired result is at- 
tained, and this is the method which is adopted. It is done 
as follows: Examining Fig. 3 you will observe there is a wire 
coil around the top part of the poles of the field magnet. This 
wire connects with one brush, passes thence to one end of coils 
of resistance wire, known as the "field rheostat," and from the 
other end of these coils to and several times around one of the 
poles of the field magnet, across the air gap to and several times 
around the other pole of the field magnet, and thence to the 
opposite brush. This circuit is known as the "field circuit" 
or "shunt field circuit." 

Now, it is a well known fact if a wire be wound around the 
poles of a magnet and an electric current be passed through 
the coil thus formed, the strength of the magnet will be in- 
creased; in other words, the magnetic field between its poles 
will be made more dense and powerful, or, in other words, 
the lines of magnetic force or the magnetic flux will be made 
greater; and this will continue as the current is increased until 
the point of saturation (iron is said to be "saturated" with 
magnetism when it will receive no more) is reached. 

As applied to the dynamo, the operation of the field circuit 
is as follows: In starting up, the armature is revolved and 
brought up to speed by an engine or some other source of 
power. The armature coils cutting through the weak field 
created by the residual magnetism generate a slight voltage, 
and, the resistance of the field rheostat (See Fig. 3) having 
first been eliminated by means provided, a current is set up 
in the field coils, which, in compliance with the facts before 
set forth, instantly increases the strength of the magnetic 
field, and thus the armature coils are made to cut a greater 
number of lines of magnetic force per second and the voltage 
is increased, and so on until the voltage at which the machine 
is intended to operate has been reached, whereupon the handle 
of the field rheostat is moved, and resistance is cut into the 
field circuit in such amount as will just regulate the flow of 
current in the field circuit to the value which will hold the 
strength of the magnet field at a point which will cause 
the armature to cut just enough lines of force per second to 
maintain the desired voltage. 

It will, of course, be readily seen that as the load on the 
generator changes an alteration of the strength of the magnetic 


field will be necessary, or, in other words, variations in load 
of the generator will require the altering of the amount of 
resistance in its field circuit, which in some dynamos is ac- 
complished automatically, while in others it must be done 
by hand. 

All the foregoing applies in practice to the shunt-wound 
dynamo, and also very largely to the compound wound dyna- 
mo, but, no matter what the type of generator may be, the 
principle set forth holds good. 

The current for the field circuit is taken direct from the 
armature of the generator, but this comprises a very small 
fraction of the total output of the machine considerably less 
than 10 per cent. 

It is not designed to do more than give a comprehensive 
understanding of the method by which electricity is generated. 
There are many excellent works on dynamo action and con- 
struction, which may be consulted at the public library of 
your city and the student can go as far as he likes in such 
matters. In this work I can only find space for such practical 
things with relation to dynamos as may be expected to be of 
direct assistance to operators who are obliged to manage and 
care for generators or a motor generator set. 


Direct current, commonly called "D. C.," acts continuously 
in one direction, presumably from positive to negative. The 
electrical impulse or, putting it another way, the flow of cur- 
rent is, theoretically, outward from the positive brush of the 
generator to the positive wire of the circuit, along that wire 
to and through the various lamps, motors, etc., to the negative, 
and back on the negative wire of the circuit to the negative 
brush of the generator. Direct current is very seldom of 
higher voltage than 500, since above that pressure it becomes 
exceedingly difficult to effectively insulate the commutator 
bars of the generator from each other. Another reason why 
we do not find D. C. at high voltage lies in the fact that after 
leaving the generator its pressure cannot be raised without 
the use of machines having moving parts, which is impractical 
by reason of the expense of installation and operation, as well 
as the necessary loss inherent in such a device. 

Alternating current is commonly known by the abbrevia- 
tion "A. C." As has already been set forth, the current in the 
armature of all generators is alternating; that is to say, the 


current in the armature coils constantly reverses its direction, 
and "alternating current" (A. C.) is nothing more or less than 
the unrectified current which is sent out on the circuit just as 
it is generated in the armature coils of the dynamo, so that 
the current in the whole circuit reverses its direction as often 
as the current is reversed in the armature coils of the dynamo. 

There are several reasons why A. C. is very largely used, 
the main one being the fact that it may be generated at rela- 
tively high pressure; also the pressure (voltage) may be 
readily increased or reduced after the current has left the 
dynamo and this may be accomplished by means of a very 
simple device known as a "transformer," which has no mov- 
ing parts, requires practically no care or attention, lasts in- 
definitely if not overloaded, and accomplishes its work of in- 
creasing or decreasing the voltage with comparatively little loss 
of energy. 

The advantage of high voltage lies in the fact that while a 
wire of given size is rated at a certain, definite number 
of amperes and no more (See Table 1, Page 42), it will carry 
those amperes at any voltage. Electric energy, by which is 
meant the ability of the current to perform work, is measured 
in "watts." One watt is equal to 1/746 of a horse power. It 
therefore follows that 746 watts is equal to 1 horse power. 
Watts are found by multiplying volts by amperes, thus: 5 
amperes at 110 volts equals (5 X HO) watts. Horse power 
equals volts multiplied by amperes divided by 746. 

Referring to Table 1, Page 42, we find that a No. 6 rubber 
covered wire must not be allowed to carry more than 50 am- 
peres of current. Now suppose .we have a No. 6 wire carry- 
ing 50 amperes at 110 volts: 110X50=5500 watts, which 
divided by 746 (watts in a horse power) gives us approx- 
imately iy-2. h.p. as the limit of power which can be conveyed 
on a No. 6 r.c. wire charged at 110 volts pressure. On the 
other hand, suppose we have the same No. 6 r.c. wire carry- 
ing 50 amperes at 2000 volts pressure. We then have 2000 X 
50 = 100,000 watts, which divided by 746 equals almost 135 h.p., 
now being conveyed over a No. 6 r.c. wire which was loaded 
to capacity with 7^2 'h.p. when the pressure was 110 volts. 

From the foregoing it will readily be seen that there is 
enormous saving in copper (wire diameters) effected by using 
high voltage. This is a particularly important item if the 
power (current) is to be conveyed any considerable distance. 
To convey 1000 h.p. five miles by means of 110 volts pressure 
would entail an enormous outlay for wires of large size, since 


it would require nearly 7000 amperes, whereas with the current 
at 10,000 volts only about 75 amperes would be necessary. 

As has been said, A. C., unlike D. C., does not flow con- 
tinuously in one direction, but, quite the contrary, flows in 
one direction and then reverses and flows in the opposite. In 
other words, the current flows one way for a small fraction of 
a second and then reverses itself and flows in the opposite 
direction for an equal space of time, the period of flow in 
either direction varying from 1/50 to 1/266 of a second, accord- 
ing to the way the generator is designed. Two periods of 
flow that is to say, the period during which the current 
flows in one direction and reverses itself and flows back 
are called a "cycle." See definition of cycle, page 22. 

Alternating current dynamos may be designed to pro- 
duce current of any given number of cycles per second, the 
determining factor being the use the current is to be put to. 
Where light only is produced, the current frequency (number 
of cycles per second) may be quite high; sometimes as much 
as 133 cycles (266 alternations) per second; but cf late years 
the use of current frequency in excess of 60 has been almost 
entirely abandoned. 

Where the current generated is to be used entirely for 
power purposes a low frequency is much preferred, for the 
reason that it is more economical for driving motors. Power 
current runs as low as 25 cycles per second, whicL is the ideal 
current to apply to motors. Twenty-five cycles per second, 
however, is unsatisfactory for incandescent or arc lighting, 
since the alternations are so far apart that there is a notice- 
able flicker in the light. Light and power companies long ago 
discovered the fact that 60-cycle current produces very satis- 
factory results in lighting, and is at the same time fairly 
economical for power purposes. For this reason practically 
ajl generators designed to provide both light and power are 
what is known as 60-cycle. machines. 

It is essential that the operator get a clear understanding 
of these things, since more and more they are called upon to 
handle motors and generators, and moreover in some localities 
and under some conditions problems arise which can only be 
solved by one conversant with this subject. The action f 
alternating current is usually expressed by diagram, such as 
that shown in Fig. 4, and I will now try to help you to 
understand how to trace out the real meaning of such dia- 
grams. Indeed, it is very necessary that you do understand, 
because when one studies matters electrical, he is constantly 


confronted with diagrams of this character, and if unable to 
trace out their meaning is greatly handicapped in his study. 

Let us consider Fig. 4. In its length the horizontal line 
represents time, and in its position with relation to the trian- 
gles above and below it represents zero voltage, or, in other 
words, no voltage, or, in other words, it represents the point 
at which the alternations of the current are completed and 
the voltage and amperage are both at zero. 

From to 1 represents the time of one alternation, which 
with 60-cycle current would be 1/120 of a second; the rise and 
fall of voltage in that alternation being represented by the 

Figure 4. 

triangular line above the horizontal line which leaves 0, 
mounts upward and comes back down to 1. The vertical 
column of figures represents voltage. Turn back to Fig. 2 and 
examine it and the text matter dealing therewith, so that the 
action of an armature coil will be fresh in your memory. 
Remember that when the coil in Fig. 2 is in the position 
shown, it is generating maximum voltage, and, conversely, 
when standing straight up and down it is in what we call the 
"neutral plane," and for an infinitesimal fraction of a second 
is generating nothing. Now, coming back to our diagram, 
Fig. 4, where the line of the triangle leaves and mounts up- 
ward, the coil of the armature is beginning to cut lines of 
force in increasing number, and the voltage is rising and con- 
tinues to do so until the coil is cutting the maximum lines of 
force, at which time the voltage has reached 110. Meanwhile 
time equal to half of an alternation, or, 1/120 -r- 2 = 1/240 of 
a second, has elapsed. Now the armature coil, begins to pass 


out of the magnetic field, and the voltage decreases until, fol- 
lowing the right-hand line of the triangle down to 1, it is at 
zero, and the current reverses. If we now follow the line on 
down on the left-hand side of the lower triangle and back up 
to 2, we will have traced the action of two alternations, or 
one cycle of current, and during that time 1/60 of a second 
will have elapsed. Now, in your imagination, draw a pencil 
point from to 1, and another pencil point round the upper 
triangle, and then continue the first pencil out on to 2 and 
run the other pencil point down around the lower triangle. 
If you could draw one pencil point from to 2 in 1/60 of a 
second, and in the same length of time trace the two triangles, 
one above and one below the line, to 2, with the other pencil 
point, you would have exactly typified the action of one cycle 
of alternating current, both as to time and rise and fall of vol- 
tage and amperage. 

With 25-cycle current, the action would be precisely the 
same, except that from to 2 would represent 1/25 of a sec- 
ond, instead of 1/60 of a second, and the action of the current 
therefore would be just that much slower. 

In studying the above get the fact clearly fixed in your 
mind that, while the action is almost inconceivably rapid, still 
it is a fact that with plain, single-phase alternating current, twice 
during each cycle, or one hundred and twenty times every second, 
there is absolutely no voltage, amperage, or anything else on the 
line. This is hard for the mind to grasp, since it is very difficult 
for the mind to accustom itself to such extreme rapidity of 

The student may ask: "Well, if it is a fact that there is no 
voltage or amperage on the line twice during each cycle, how 
does it happen that the light from alternating current is con- 
tinuous?" In reply I would say that the light is not contin- 
uous, but the action is so enormously rapid that the effect of 
one alternation blends in the next, so that with 60-cycle current 
the effect is that of continuous, uninterrupted, even illumina- 
tion, but if the current be 25-cycle, then the action is slow 
enough that the eye can detect an uneveness of illumination, 
in the form of flicker, and that is why very low cycle alter- 
nating current, while ideal for power purposes, is objection- 
able and unsatisfactory for lighting. 

In handling alternating current we run into many complica- 
tions, one of which is the fact that we have single-phase, 
two-phase, and three-phase current to deal with. In Fig. 4 
we have traced the action of alternating current. In Fig. 5 
we see, at A, a diagrammatic representation of two-phase 



current. Two-phase and three-phase current is produced 
by a peculiarity of the winding of the generator. How- 
ever, for the purpose of a clear understanding, we will assume 
that we have two generators, producing current of the same 
cycle, with their armatures coupled rigidly together in such 
manner that when the current flow of one is at zero the vol- 
tage of the other is at maximum. We will thus have a two- 
phase current delivered, and the voltage of such a circuit will 
never be at zero, since when the current generated by one of 
the machines is at zero the other is at maximum. Now, if we 
couple the shaft of a third dynamo to the shafts of the other 

Figure 5. 


two, in such manner that the voltage rises and falls, as shown 
at B, Fig. 5, we shall have three-phase current. Two-phase 
current ordinarily employs four wires (two separate circuits) 
for its distribution. Its advantage lies in the fact that the 
two currents, acting like the piston of a double engine, give 
a steady instead of an intermittent pull on the armature of 
motors. Three-phase current requires three wires for its 
distribution. It is the ideal system for transmitting energy, 
through any distance, for power purposes. . It gives a prac- 
tically steady pull on the motor armature. Neither the two 
nor three phase systems has any particular advantage over 
single-phase 60 cycle current for lighting purposes. 

Electrical Terms 

IT is essential that the operator have a complete under- 
standing of certain terms used in connection with elec- 
trical work. It is quite difficult to impart a clear under- 
standing of some of the terms, but we will nevertheless do 
our best to make the matter at least reasonably clear. 

Work is the term used to describe the act of overcoming 
resistance through a certain distance. It is measured in foot- 
pounds. See foot-pounds. 


Foot-pounds. A foot-pound is the amount of work done or 
energy consumed in raising a weight of one pound one foot, 
or the equivalent, such as, for instance, raising one-half 
pound two feet, or raising two pounds one-half foot. It may 
also be described as overcoming a pressure of one pound 
through a distance of one foot. 

Coulomb. The coulomb is used to measure the quantity 
of current flowing in one second. It is the number of ^am- 
peres of current passing in one second. It is the product of 
the amperes times seconds, thus: 

10 amperes flowing in 1 second multiplied by 1 
second equals 10 coulombs; 10 amperes flowing 
for 2 seconds equals 20 coulombs. 

Volt-Coulomb. The volt-coulomb is the electrical unit of 
work. It is that amount of work performed when one ampere 
of current flows for a period of one second in a circuit whose 
resistance is one ohm, when the pressure is one volt. 

Ampere-Hour. One may draw a certain quantity of water, 
say a gallon, from a hydrant in one minute, or in ten min- 
utes, but, regardless of the time consumed in drawing the 
water, it is still one gallon, no more and no less. The 
same holds true in dealing with electric current. A certain 
given quantity may be used in one minute, or in ten minutes. 
The current flowing in any circuit is the relation of the quan- 
tity flowing to the time during which it flows, or, expressed 

As has been said, coulombs equals amperes multiplied by 
seconds, or, 

2 amperes X 10 seconds = 20 coulombs. 
10 amperes X 2 seconds = 20 coulombs. 

1 ampere X 20 seconds = 20 coulombs, and so on. 
By the foregoing you will be able to calculate that if one 
ampere flows for one 'hour we would have 1 ampere X 60 sec- 
onds = 60 coulombs, and 60 coulombs X 60 minutes = 3600 cou- 
lombs, so that one ampere flowing for one hour equals 3600 
coulombs, and 3600 coulombs are, therefore, one ampere- 
hour, or a flow of 2 amperes for one-half hour would be one 
ampere-hour, or a flow of 4 amperes for 15 minutes would be 
one ampere-hour, since in either case 3600 coulombs would 
have been used. 

Ampere. Ampere is the unit rate of current flow. It repre-^ 
sents the quantity of current flowing through a circuit, pre- 
cisely the same as gallons or barrels represent the quantity 
or volume of water flowing through a water pipe. 


Operators should carefully consider the distinction between 
the ampere and the coulomb. The term coulomb is not much 
used, but it is nevertheless one of much importance, since it 
measures the quantity of current passing in a given time. 

The ampere is such a rate of flow as would transmit one 
coulomb per second through a resistance of one ohm, under a 
pressure of one volt; a current of such strength as would 
deposit .005084 grain of copper per second. 

Volt The volt is the unit of electric pressure. It is the 
electro-motive force induced in a conductor, usually an arma- 
ture coil, which is cutting 100,000,000 lines of magnetic force 
per second. It is the term used to designate the strength of 
the affinity of one wire of an electric circuit to and for the 
other wire. It is the term used to designate and describe the 
intensity of electrical action. It is the term used to designate 
that quality or property of the electric current, or electric 
action, which corresponds to pressure in a steam boiler, or in 
a water pipe. 

Ohm. Ohm is the unit of resistance. It is the term used to 
designate and measure the opposition offered to the flow of 
electric current. It is the amount of resistance offered by a 
column of mercury 106 centimeters in length, having an area 
of cross section of one square millimeter, at degrees centi- 
grade, or 32 degrees F. This is the established international 
value of the ohm, designated as the "Legal Ohm." 

Watt. Watt is the unit of power. It is obtained by multi- 
plying volts by amperes: 1 volt X 1 apmere = 1 watt, hence, 
10 amperes at 110 volts would be, 100 X 10= 1100 watts; 746 
watts equal 1 horse power (h.p.). See kilowatt. See watt- 

Kilowatt.- Kilowatt is merely a term of convenience, mean- 
ing 1000 watts. It is 1000 -f- 746 = 1.34 ihorse power. 

Watt-Hour. One watt-hour represents the amount of work 
performed by one ampere of current at one volt pressure dur- 
ing a period of one hour, hence, 4 amperes at 110 volts would 
be 440 watts, and when that amount of energy has been ex- 
pended for a period of one hour it would be 440 watt-hours. 

Horse-Power. One horse-power (h.p.) equals 33,000 foot- 
pounds of work per minute. It is the theoretical amount of 
work one strong draft horse is supposed to perform if a block 
and tackle be attached to a weight of 33,000 pounds and the 
tackle be of such proportion that the horse can, by exerting 
his full strength, just raise the 33,000 pounds one foot while 
walking outward pulling on the rope for a period of one min- 
ute. Under these conditions one horse-power has been ex- 


erted during that minute. That is the theory of the thing. 
One horse-power-hour is the amount of work exerted by one 
horse during one hour, or by 60 horses during one minute, or 
by 3600 horses during one second. In electrics 746 watts is 
supposed to represent the raising of 33,000 pounds one foot in 
one minute, or, in other words, one horse power. The unit 
was established as follows: 1 watt is equivalent to 1 joule 
per second (the joule is the practical C.G.S. unit of electrical 
energy. One joule is equal to .73734 of a foot-pound, or, .00134 
h.p. -seconds; it is the quantity of electric energy necessary 
to raise the potential of one coulomb of electricity one volt in 
pressure) or 60 joules per minute, and 1 joule is equal to 
.73734 of a foot-pound, therefore 60 joules = 60 X .73734 = 
44.24 foot-pounds. Now, since one horse-power equals 33,000 
foot-pounds per minute the electrical equivalent would be 
33,000^-44.24 = 746 watts. 

Resistance is that property of an electrical conductor by 
which it resists the flow of electric current. It is quite similar 
in its effect on electric current to the opposition water en- 
counters in flowing through a pipe by reason of friction with 
the walls of the pipe. 

Polarity. Polarity is the difference in condition between 
the positive and the negative electrodes of a battery, or of two 
wires attached to the positive and the negative electrodes of 
a battery. It is the difference in condition between the two 
terminals of a working dynamo, or between the wires attached 
thereto. It may be described as representing the ability of 
the two battery electrodes, dynamo terminals, or wires at- 
tached thereto, to perform work. Positive : from which electric 
impulse comes or "flows." Negative: opposite of positive. 

Short Circuit. The term applied to a direct, accidental cur- 
rent-carrying connection between two wires of opposite 
polarity, by means of which the current is enabled to skip a 
portion of its appointed path. 

Shunt Circuit. A subsidiary or secondary circuit on any 
part of a main circuit, by means of which a portion of the 
current leaves the main circuit and flows through the sub- 
sidiary or secondary circuit, as, for instance, the field magnet 
circuit in Fig. 3, page 10. 

Commutator. A device attached to the armature of a dy- 
namo by means of which the alternating current generated in 
the armature coils is changed into direct current for delivery 
to the outside circuit. 


Direct Current. Current which flows continually in one 

Alternating Current. Current which flows alternately in 
one direction and then in the opposite, the time of the flow in 
either direction varying from 1/50 of a second to 1/226 of a 
second, according to the construction of the generator. 

Conductor. A wire or metal bar used to convey electric 

Cycle. Events following each other in regular succession. 
One-half the number of changes in direction of alternating 
current per second. Two complete alternations of alternating 

Dimmer. An adjustable choke or resistance coil used for 
increasing or decreasing the resistance in an incandescent 
circuit gradually, so that the incandescent lamps attached 
thereto will be extinguished or lighted gradually. An adjust- 
able rheostat for use on incandescent light circuits. 

Electric Motive Force. Another name for voltage, and the 
one commonly employed in text books. 

Ground. A connection between wires of opposite polarity 
through the ground, having resistance low enough to allow 
current to pass from one wire to the other. 

Static Electricity. A form of electricity which is generated 
by friction. 

Main Feeder. The street circuit entering a district to 
which feed wires supplying the various streets are attached. 

Street Mains. Feed wires supplying individual house mains. 

Electro Magnetic Field. The field produced by an alter- 
nating electric current or by an electric magnet. 

Magnetic Field. That region of magnetic influence which 
surrounds the poles of a magnet or wire carrying A. C. 

Fuse. A short length of wire interposed in an electric cur- 
rent, the same being of some alloy which will melt (thus 
breaking the circuit and stopping the flow of current) at a 
temperature much less than that necessary to raise the tem- 
perature of a copper circuit wire to the danger point. Fuses 
usually melt at less than 300 degrees F. 

Galvanized Iron Wire. An iron wire coated with zinc, in 
order to resist the action of corrosion. 

Graphite. A condition of carbon in which it becomes an 
excellent lubricant, able to withstand very high temperature. 


In this condition it forms the "lead" of the ordinary lead 

Induction. The influence which a mass of iron charged 
with alternating current exercises upon surrounding metallic 
bodies, without having any actual metallic connection there- 

Insulation. The employment of any material having such 
high resistance that electric current is unable to pass through 
to the earth, or other current carrying substance, and thus 
reach a wire of opposite polarity. Rubber, porcelain and 
glass are examples of insulating materials. 

Magnetic Saturation. That point at which the power of a 
magnet cannot be further increased. 

Torque. That force which tends to produce a rotary move- 
ment around an axle, as the pulling or rotating of an electric 
motor's armature upon its shaft. The force applied to the 
rim of a dynamo pulley by a belt. Turning force. 

Transformer. An induction coil by means of which the vol- 
tage of a circuit may be changed without materially altering 
its wattage. A step-up transformer is one which transforms 
a current of given amperage and voltage to a current of less 
amperage and higher voltage. A step-down transformer is 
one which transforms a current of given amperage and vol- 
tage to a current of less voltage and higher amperage. 

Ampere Turn. A unit of magneto-motive force equal to 
the force resulting from the effect of one ampere passing 
around a single turn of a coil of wire. 

Voltmeter. Ah instrument by means of which the voltage 
or electro-motive force of a circuit is measured. 

Ammeter. An instrument by means of which the current 
flow in a circuit is measured in amperes. 

Wattmeter. An instrument by means of which the power 
being consumed in a circuit is measured in watts. 

Current Frequency. The number of cycles per second. 

Efficiency. The term used in describing the loss inherent 
in transformers, motors, generators, generator sets, etc. Elec- 
trically it is the relation of the wattage taken from the line to 
the wattage actually employed in the work in hand. For in- 
stance: If a motor takes 3000 watts from the line and only 
exerts a pull on the thing it is driving equal to 2000 watts, 
then its efficiency would be the percentage found by dividing 
2000 by 3000, and 2000-^3000 = .666 or 662/3 per cent. 


Circuit. The term commonly applied to wires of opposite 
polarity to which are attached other power consuming circuits 
or lamps, motors, etc. 

Synchronism. Synchronism is the term used to describe 
the action of A. C. alternations with relation to each other. 
Synchronism is sometimes referred to by electricians as "keep- 
ing step." It means that where two or more alternating cur- 
rents are coupled together, as in two or three phase current, 
their voltage values must rise and fall constantly with fixed 
relation to each other, as shown in Fig. 4, Page 16. In order 
to produce two or three phase current the voltage values must 
remain absolutely in step or synchronism with each other. 
When a motor is run in synchronism with a generator it 
means that the voltage value of the alternations in the arma- 
ture of the motor arc and must remain absolutely identical 
with the voltage value of the alternations in the armature of 
the generator. Once you grasp the real meaning of Fig. 5 
the understanding of synchronism will be easy, therefore 
study Fig. 5. 

An Explanation of Electrical Terms, 

I HAVE given you the definition of certain electrical terms 
which the operator is likely to come into contact with in 
his work. In order to convey a more complete under- 
standing of the true meaning of certain ones of these terms, 
however, something more than a mere definition is necessary, 
therefore 1 shall elaborate by amplifying certain definitions 
in the form of an explanation. 

Polarity. Polarity and potential mean the same thing. 
When a wire is attached to one terminal of a working dynamo 
and another wire is attached to the opposite terminal of the 
same dynamo there is an electrical condition in these wires 
which enables them to perform work, or, more correctly, to 
cause a motor to which they are attached to perform work, or 
cause a lamp to which they are attached to give off light. This 
electrical condition is called "polarity," or "potential." It is 
the affinity one wire of an electric circuit has for the other 
wire of this circuit. It represents the inclination of the cur- 
rent to flow from one wire to the other wire, and this inclina- 
tion is so strong that in order to pass from one wire to 
the other the current will perform labor, and lots of it. When 
dealing with direct current one wire is always positive and 


the other is always negative; when dealing with alternating 
current each wire is alternately positive and negative many 
times each second. 

Voltage (E.M.F.). Electric current may be said to have 
both pressure and volume, and in its action in both these re- 
spects, as well as with regard to friction, electricity is very 
similar to and may be compared with water or steam. We 
must, however, carefully remember, when using these com- 
parisons, that they only hold good as applied to the laws of elec- 
trical action which have been determined by experiment. In 
other words, the similarity between electricity and water or 
steam exists only in their similarity of action. Water may be 
perceived by the senses; we can feel it and watch its action, 
whereas electricity is an absolutely impalpable substance, 
which cannot be perceived by any sense except that of touch, 
and even then it cannot be felt except through the "shock" 
occasioned by its passing over the tissues of the body. (We 
can see electric light, yes, but that is only the effect of the 
current, not the current itself.) 

Voltage corresponds in effect or in its action to the pressure 
of water in a pipe, or to the pressure of steam in a boiler. A 
dry battery, such as is used for electric bells, has a pressure of 
approximately one volt, and it imparts that pressure to wires 
connected to its terminals, so that if you attach two wires to 
such a battery they will, at any portion of their length, have 
a pressure of one volt. Now, if you take a second battery 
and connect its zinc with the carbon of the first battery by 
means of a short piece of wire, and then attach 'two other 
wires to the two remaining binding posts, you will have what 
is known as "series" connection, and a resultant pressure of 
two volts between the two wires. A third battery connected 
in series would raise the pressure to three volts, and so on, 
indefinitely. Instead of using batteries for producing light 
and power, which would be entirely impractical, we use a 
machine called a dynamo, each one of which is designed and 
built to produce a certain voltage, which may be anywhere 
from one to five hundred volts D. C, or from one to six 
thousand A. C. 

Remember that voltage corresponds to pressure, and is 
similar in its action to pressure in a steam boiler, but that 
voltage acts only between the positive and negative wires of 
the dynamo which generated it, and that the positive attached 
to one generator has no affinity or attraction to or for the 
negative attached to another dynamo, or for the ground, ex- 
cept as it offers a path to the negative of the generator to 


which the positive is attached. Get this fact firmly fixed in 
your mind. Ninety-nine non-electricians out of every hundred 
believe current generated by a dynamo seeks to escape into 
the ground. This is not so, except as the ground offers a path 
between two wires of opposite polarity. If the positive or 
negative side of a dynamo generating 5000 volts be thoroughly 
and completely insulated (never actually the fact in practical 
work) you could stand on wet ground and handle the bare 
wire of the other side with your bare hands in perfect safety. 

Ampere. Ampere is the term used to denote quantity. It 
represents the volume of current flowing through, or along a 
wire, just as gallons or barrels represent the quantity of 
water flowing through a pipe, or cubic inches the volume of 
steam flowing. As a matter of fact we do not actually know 
that anything flows in or along the wire of an electric circuit. 
Eminent electricians say there is an actual flow; other equally 
eminent electricians say there is not, but that what we con- 
sider as current flow is really a "molecular bombardment." 
With these highly technical questions, however, we have 
nothing to do. For our purpose it is sufficient to say that current 
flows along the wire, just exactly as water flows in a pipe. The 
work performed is accomplished by the voltage or pressure 
working through the amperage or volume, and it is the 
pressure or voltage which is consumed never the amperes. 
Therefore, the higher the voltage or pressure, the greater 
amount of work a given volume of current can perform. For 
instance: If you supply a steam engine with steam at fifty 
pounds' pressure it will consume a certain given quantity or 
volume of steam to each stroke of the piston, according to the 
cubic capacity of the cylinder, and this quantity of steam at 
fifty pounds pressure will do a certain given amount of work. 

Now, if you raise the pressure of the steam to one hundred 
pounds the engine will perform twice as much work, but will 
not consume any greater number of cubic inches of steam. 
And so it is with electric current: One-half of an ampere at 
50 volts will do a certain amount of work, but the same one- 
half ampere at 100 volts will do just twice as much. In other 
words, the amperage or volume of current is simply the 
medium through which the voltage or pressure (E.M.F.) acts, 
or works. In a steam engine, with the steam at given pres- 
sure, you can increase the power of the engine by either in- 
creasing the size of the engine cylinder, or by increasing the 
pressure of the steam. In a water motor you can increase 
the capacity to do work either by increasing the size of the 
motor or the pressure of the water. The same thing holds 


true with electricity. You can increase its capacity to do 
work either by increasing the volume of current (amperage) 
or by increasing the voltage. To perform a given amount of 
work with a low pressure (voltage) a large volume (amper- 
age) is necessary, but if the voltage be high the same amount 
of work can be performed with much less volume of current. 
In fact, the number of horse power of work performed by 
electric current is represented by the voltage times the am- 
peres, divided by 746. 

Ohm. Water in passing through a pipe encounters resist- 
ance, by reason of the rough sides of the pipe, as well as by 
reason of the internal resistance of the water itself. This 
resistance tends to retard the flow. Precisely the same is 
true with electricity. In passing through a wire electric cur- 
rent encounters resistance, and this resistance tends to retard 
the flow of current. It is measured in ohms, the definition of 
which is given elsewhere. The effect of resistance is to pro- 
duce heat. In a water pipe the resistance increases as the 
volume of water passing through the pipe is increased, or as 
the pipe is made smaller in relation to the volume of water 
flowing. It decreases as the pipe is made larger with refer- 
ence to the volume of water flowing. The same thing is true 
of current. Having a wire of given area, the resistance in- 
creases as the current flow becomes greater, and decreased as 
the current flow becomes less, or, having a given current flow 
the resistance increases as the diameter of the wire is made 
less or its length is increased, or decreases as the diameter 
of the wire is made greater or its length is decreased. 

Watt. Watt is the unit used to measure the amount of 
electrical energy expended the amount of work actually per- 
formed. It is found by multiplying the voltage by the am- 
perage, and is transformed into horse power by dividing by 
746, since 746 w,atts equal one horse-power. 

For example: If we have 10 amperes flowing at 110 volts, 
the amount of energy expended would be equal to 110 X 10 = 
1100 watts, which, divided by 746= 1.47 h. p. If, on the other 
hand, we had 110 amperes flowing at 10 volts the result would 
be the same. But if we had 10 amperes flowing at 10,000 volts 
then we would have electrical energy expended (work per- 
formed) as follows: 10,000X10=100,000 watts -f- 746 = 134 
h. p. 


Use of Electrical Terms in Calculation 

IT is quite problematical as to how much use the average 
operator will be able to make of electrical terms in mak- 
ing calculations, since, in order to find an unknown 
quantity he must know two other quantities. In order to cal- 
culate the number of amperes flowing in a circuit it is neces- 
sary the voltage and resistance in ohms be accurately known, 
and, while the operator usually knows about what the voltage 
is, the resistance is seldom a known quantity, or one which 
the operator can readily ascertain with any degree of ac- 
curacy. To find the number of ohms resistance, the operator 
must know the exact amperage and voltage, which he can, if 
necessary, obtain by means of a reliable voltmeter and am- 
meter. To find the voltage he must know the exact resistance 
in ohms and the exact amperage. But, notwithstanding the 
fact that only two of these quantities are usually known to 
the operator, and those two often only known approximately, 
the operator ought to understand how to make electrical cal- 
culations, particularly with relation to his projection arc cir- 
cuit, and I shall therefore give a somewhat extended explana- 
tion of the method. 

The operator must fix firmly in his mind the fact that where 
the projection lamp circuit is concerned the resistance does 
not lie wholly in the rheostat, or whatever takes its place. 
The wires, lamp arms and carbons offer small resistance, but 
a very considerable portion of the total is in the arc itself. 
The resistance of the wires, lamp arms and carbons may, for 
ordinary purposes, be neglected, but unless the resistance of 
the arc itself be taken into consideration a very serious error 
will result. 

When making electrical calculations it is customary, for the 
sake of brevity, to use the letters E, C and R. E stands for 
"electro-motive force," which is merely another name for 
voltage, hence E stands for voltage; C stands for current flow, 
meaning amperes, hence C stands for amperes; R stands for 
resistance in ohms, hence R stands for ohms. 

The operator should also remember that in a common frac- 
tion the horizontal line always means "divided by," thus ^ 
really means 1 4- 2. But I think I hear some one say you 
cannot divide one by two. Oh, yes, you can. It is done 
thusly: We put down the one, followed by a period, called a 
"decimal point," and then add ciphers, thus: 1.00. We now 
have 1.00 with a decimal point between the one and the two 
OOs, and 1.00 -4- 2 = .50, or, .5, which is exactly the same thing 


as 50/100, 5/10, or 1/2. The rule .is to count the figures or 
ciphers to the right of the decimal point in the number being 
divided, and then, beginning at the last figure of the result, 
count an equal number, and place the decimal to the left of 
the last figure counted. If there are not enough figures in the 
result to do this, then add ciphers to the left. 

When dealing with formulas, means that the quantity 


represented by E is to be divided by the quantity represented 
by C, E being the voltage and C amperes. If there be two 
or more quantities above or below the line, with no sign be- 
tween them, it means they are to be multiplied together, thus: 

means that E (volts) is to be divided by C (amperes) 

C R 

E 15 

multiplied by R (ohms), means that after 15 has been 


subtracted from the quantity represented by E (volts) it is 
to be divided by the quantity represented by C (amperes). 
The student will be greatly benefited if he will practice writ- 
ing out formulas of this kind in letters, substituting quantities 
in figures and working them out. 

Ohms law sets forth the fact that the number of amperes 
flowing are equal to the voltage divided by the resistance in 


ohms. We, therefore have = C, or, in other words, volts 


divided by ohms equals amperes. It then follows that if 

= C, C multiplied by R must equal E. It also follows that 


= R. It works out as follows: We know that the ordinary 


110-volt 16 c.p. carbon filament incandescent lamp requires 

approximately one-half ampere of current to bring it up to 

candle power. What is its resistance? Using the formula 

E 110 volts 

= R, substituting figures, we have = 220, 

C .5 of an ampere 

the number of ohms resistance in the filament of the lamp. 


E 110 

Again applying the formula = C, we have = .5, or ^2, as 

R 220 

the amperage 110 volts will force through 220 ohms resistance. 
It seems to me all this is simple enough of understanding and 
application, but to make it yet more plain I will take the 

formula = R, which means voltage divided by amperes equal 


ohms, so that if the voltage be 50 and the amperes 10, E would 
mean 50, C 10, and R would be 50 -^ 10 = 5, but if the voltage' 
be 110 and the amperage 5, then E would mean 110, C 5 and 
R would be 110 -i- 5 = 22 ohms. 

When, however, we come to consider the projection arc 
circuit, a new element enters in the shape of the resistance of 
the arc itself, and if we propose to be absolutely accurate we 
must consider also the resistance of the carbon arms, wires, 
etc., but that degree of refinement is seldom or never neces- 
sary in a projection circuit calculation. 

In leaping the air gap between the carbon tips of the arc 
lamp the current encounters high resistance. In overcoming 
resistance voltage is consumed, as will be more thoroughly 
set forth and explained under "Resistance," Page 34. Tn other 
words, when current-flow is opposed by resistance, and that 
resistance is overcome, there is a consequent drop in pressure 
or voltage; pressure has been used, or consumed in the proc- 
ess. The resistance of the arc, consequently, the voltage 
drop in overcoming the resistance, is proportional to (a) 
length of arc; (b) size and characters of the carbons; (c) kind 
of core in the carbon; (d) number of amperes flowing. All 
these factors enter very decidedly into the equation, but very 
largely the resistance encountered is directly proportional to 
the length of the arc. 

For reasons not necessary to enter into at this time the 
D. C. arc, for a given amperage, is longer than the A. C. arc. 
It, therefore, follows that its resistance will be higher. The 
accepted theory is that all voltage is consumed at the arc. 
Whether or not this is true is a highly technical question, 
which it would be unprofitable to discuss in these pages. We 
shall accept the theory. Therefore the rheostat or whatever 
takes its place must cut down the voltage to just that pressure 
which the resistance of the arc will consume when burning 

When an ordinary D. C. projection arc is operating at its 
best it consumes about 48 volts. The D. C. arc voltage varies 


from 45 to 55, but 48 is a fair average. In other words, the 
current must reach the arc at that pressure, and that pressure 
will be consumed in the arc. Ordinarily it is spoken of as 
"48 volts drop across the arc." What is the resistance of 
such an arc operating at 40 amperes? Knowing the voltage 

(48), and amperage, we apply the formula = R, and have 


48 -T- 40 = 1 1/5 ohms arc resistance. Let us prove this out. 
Suppose the line voltage to be 110. The total resistance must 

equal ( = R) the voltage divided by the amperes flowing; 


therefore, the amperage being 40, the resistance must be 
110 -r- 40, or 23/4 ohms. We have seen that the arc resistance 
is 1 1/5 ohms with its voltage at 48. Subtracting the arc 
voltage from the line voltage leaves us 62, as the drop in vol- 
tage there must be across the rheostat. Again applying the 

formula ( = R), we have 62 -r- 40 = 1 11/20 as the ohmic re- 


sistance of the rheostat. Adding this and the arc resistance 
together, we have a total of (1 1/5 + 1 11/20) 23/4, as the total 
resistance, which corresponds to the total resistance necessary 
to allow 40 amperes to pass through. 

If the amperage were 45, then the total resistance, voltage 
remaining the same, must be less. If the amperage were 
less, then the resistance would necessarily be greater. The 
higher the voltage the greater must be the resistance, as will 

be seen by applying the formula = R, to accomplish a given 


current flow. Resistance is always found by application of 
the formula last quoted. 

Arc resistance, as we have said, will vary somewhat, accord- 
ing to the character of carbons and cores, the amount of cur- 
rent flowing and the arc length, particularly the latter. How- 
ever, with the D. C. projection arc we are reasonably safe in 
taking the constant 48, for the arc drop, or arc voltage, unless 
the amperage is low say 30, or less, when 45 will serve better. 
Such a standard is necessary, even though more or less in- 
accurate, since the operator sel-dom has a voltmeter with 
which to measure the arc voltage exactly. Instead of applying 



the formula = R, as it stands, we first subtract the arc 


voltage (using the standard 48), from E, which represents the 
line voltage, thus securing, at one operation, the total resist- 
ance other than that of the arc. The problem then reads, for 

E 48 
any D. C. arc above 30 amperes, - '=R, but the "R" in 


this case is the necessary ohmic resistance except that peculiar 
to the arc itself. In subtracting 48 we have accounted for the 
arc resistance. For an arc of 30 amperes, or less, the formula 

is - = R. For the ordinary A. C. projection arc, up to 60 

E 35 
amperes, the formula to be used is - = R. In other 


words we use 35 as the A. C. constant for arc voltage, instead 
of the 48 used for D. C. 

Suppose we wish to construct, or order a rheostat to deliver 
25 amperes on 125 volts line pressure, when working in series 

E 45 
with a D. C. projection arc. We use the formula - = R. 


Substituting figures for letters we have -- , which equals 


the necessary ohmic resistance of the rheostat, not taking ac- 
count of line and carbon resistance. 125 45 = 80 and 
80 -T- 25 = 3 1/5, the number of ohms resistance the rheostat 
must contain. If it were a 40 ampere arc we would subtract 
48 instead of 45. If it were an A. C. arc we would subtract 35. 
Were we to connect the same rheostat between the wires of 
a circuit carrying the same voltage without an arc in series, 
or, what amounts to practically almost the same thing, 
freeze the carbons of the arc lamp, we would then find the 
3 1/5 ohm rheostat, which delivered 25 amperes in series with 

an arc, to be delivering ( = C) 110-=- 3.2 = 34.4 amperes, 




There is a very simple formula, easy of application, which 
combines the three formulas into one. It is called the "Rule 



of Thumb." It is expressed for general use as: . 


To use the formula you have but to cover the symbol or 
letter representing the quantity desired, and what remains 
will produce the answer, thus: Suppose we wish to ascertain 
the resistance in ohms. We cover up the "R" in the formula 

and find that we have remaining, which will give R, the 


desired quantity. In using this formula on projection circuits 
the top letter must be expressed as E minus the arc voltage, 
the same as in the regular formulas, thus: 

E-48 E 45 E 35 

or for D. C. and for A. C. 


Go to your work each day 
as though it ^vere your 
first day on a new job 
and you had to make good. 



ONE of the most difficult problems confronting the oper- 
ator and the electrician is resistance. This is a factor 
which is met with in almost every phase of electrical 
work, and, so far as light be concerned, it may be said to be 
the very foundation stone of the structure. 

How Resistance Acts. In passing through a wire, current 
encounters resistance, which is, in its action, very similar to 
that encountered by water under pressure in passing through 
a pipe. When water flows through a pipe it encounters resist- 
ance directly in proportion to the size and length of the 
pipe and the quantity of water flowing per minute. This 
resistance is to some extent the result of molecular friction 
within the water itself, but mostly it is caused by friction be- 
tween the water and the sides of the pipe. In a pipe of given 
diameter, resistance increases with (a) increase of the flow, 
or volume of water, (b) increase of the length of the pipe, 
and (c) with the roughness of the inside of the pipe. Con- 
versely it decreases with decrease of the flow, the shortening 
of the pipe or with increased smoothness of pipe walls. With 
a given flow of water, resistance increases with the length 
of the pipe, the decrease in its diameter or added roughness, 
and decreases as the pipe is made larger or shorter or 

Resistance consumes pressure, and pressure is consumed 
exactly in proportion to the amount of resistance encountered. 
In the second edition of my Handbook I explained this propo- 
sition by means of a diagram, and I do not think that 
particular thing can be improved upon, therefore it is herewith 
reproduced in somewhat different form. 

In the illustration we see a water main, with a pressure 
gauge registering 100 pounds, to which are connected three 
pipes A, B, and C. On A is a pressure gauge placed right up 
close to the main pipe and another near its outer end. We 
will assume the diameter of this pipe to be one-half inch. At 
B is a short pipe of the same diameter; at C is a pipe three 
inches in diameter for ten feet of its length, with a three-foot 
extension of half-inch pipe at its end. At the outer end of 
the large pipe is a pressure gauge, with another at the end 



of the extension. Now let us consider the action. Pipe B is 
short and, being open at its end, the water spurts out with 
great force, carrying itself almost horizontal for a consider- 
able distance, thus showing that the pressure at the mouth of 
the pipe is high. The water at the end of pipe A does not 
come out with such great force, and if we examine gauge 
No. 1 and gauge No. 2 we shall find that, whereas gauge No. 1 
registers very nearly the same as the one on top of the main 
pipe, No. 2 will register far less. Gauges No. 1 and No. 2 
are on the same pipe. What is the explanation of the differ- 
ence in pressure? 

The answer is simple. It has been used up in forcing the 
water at high speed against the friction of the pipe. The 
pipe is, under the conditions, working above its normal capac- 

Figure 6. 

ity, with the result that very high resistance is developed, 
and the greater the resistance the more power (pressure) is 
consumed in overcoming it. 

Examining gauge No. 3 at the end of the large section of 
pipe C, we find that it stands almost if not quite at equal pres- 
sure with the one on top of the main, although it is ten feet 
from the main, whereas gauge No. 4, at the end of the small 
three-foot section, shows considerably less. What is the rea- 
son for this? 

Again the answer is simple. The volume of water passing 
through the short' pipe is very great as compared with its 
diameter. It is rushing through at high speed, therefore the 
friction or resistance encountered is high, with the result 
that pressure is used up very rapidly in forming the water 
against it. On the other hand, while precisely the same 


volume or amount of water is passing through the large sec- 
tion of the pipe it is moving quite slowly, hence the resistance 
it encounters is comparatively slight, and very little power 
is necessary to overcome it. 

The pressure at which the water might be would not affect 
the result, except that if it be very low not much resistance 
could be overcome. A pipe of given diameter will carry water 
up to its capacity (the capacity of a pipe may be said to have 
been reached zvhen its resistance to the flow of water becomes 
excessive, so that there is a considerable waste of power in forc- 
ing the water through} under any pressure sufficient 4:o move the 
liquid and less than that sufficient to burst the pipe. A pipe of 
given diameter will convey only a certain number of gallons of 
water per minute without excessive friction, regardless of whether 
the pressure be 10 or 100 pounds per square inch, but when the 
point is reached where resistance to flow becomes excessive, the 
normal capacity of the pipe is said to have been reached. True, 
we can still force a great deal more water through, but it will 
be at the expense of largely increased power consumption. It 
costs money to force a water pipe above its capacity, and the 
cost increases very rapidly in proportion to the excess of 
capacity; in other words, the higher the excess over capacity 
the greater the relative cost of overcoming the resistance. 

The practical method of reducing this resistance is to in- 
crease the diameter of the pipe until the desired flow is had 
with only a normal friction loss. We therefore deduce the 
rule that: 

Increasing the diameter decreases the friction, or resistance 
offered to a given flow, since the water is thus caused to move 
more slowly. 

But another equation enters 'here, viz., the length of the 
pipe. Inasmuch as friction very largely results from the 
rough side of a pipe, it naturally follows that the longer the 
pipe the more friction there will be. We have already seen 
that with a given flow as the diameter of the pipe is decreased 
(made less), the friction or resistance is increased (made 
greater), and conversely, as the diameter of the pipe is in- 
creased (made greater) the friction or resistance is decreased 
(made less). 

We may also readily see that, with a given flow: 

As the length of the pipe is increased the-friction (resistance} 
is increased, and, conversely, as the length is decreased the re- 
sistance is also made less. 

Therefore, we may increase the resistance by (a) increas- 
ing the flow of water; (b) decreasing the diameter of the pipe; 


(c) increasing the length of the pipe; (d) increasing its 

We may decrease the resistance by (a) decreasing the flow; 
(b) increasing the diameter of the pipe; (c) making the pipe 
shorter; (d) making the pipe smoother. 

All this is simple, and is or ought readily understand- 
able. And now what has been said of the water pipe is also true 
with relation to current and wires. If you substitute circuits of 
wire for the water main and for pipes A, B, and C, with volt- 
meters in place of the pressure gauges, and lamps or motors 
instead of the open pipe-end you will get precisely the same 
relative result in loss of pressure (voltage) when current flow is 
sent through the circuits. 

The voltage of the current has absolutely nothing whatever 
to do with the necessary size of wire. You could convey 
current at 10,000 volts, or 50,000 volts for that matter, on a No. 
40 wire, which is no larger than a very fine silk thread, but 
on that wire you could convey a very small quantity amper- 

Electric current in passing through wires' encounters re- 
sistance precisely the same as does water in passing through 
a pipe. A wire of given diameter will convey a certain given 
number of .amperes of current without excessive friction 
(resistance), just the same as a water pipe of given diameter 
will convey a certain given number of gallons of water with- 
out undue friction or resistance, and the point where resist- 
ance begins to rise above normal marks the "capacity" of the 
wire, just as it does the water pipe. Beyond that point the 
friction or resistance becomes excessive, and manifests itself 
in a loss of pressure or voltage. This loss in pressure has 
been consumed in forcing the current against resistance, pre- 
cisely as was the case in the water pipe. It therefore follows 
that loading wires beyond their normal capacity is expensive, and 
should be avoided for that if for no other reason, since the waste 
is registered on your meter and you will have to pay for it, ex- 
actly the same as you pay for current used in your lamps or 

But this is not all, for if you attempt to force amperage in 
excess of the rated capacity, as shown by the Underwriters' table 
(see page 42), heat will be developed, and, if the matter be car- 
ried too far (which can only be done by overf using), the wires 
may get red, or even white hot, finally burning in two entirely 
and stopping all current flow and perhaps setting fire to the 
building in the process. 


Exactly as was the case with the water pipe, with a given 
current flow the resistance of a wire is decreased as the diameter 
of the wire is increased, or its length made shorter, and is in- 
creased as the diameter of the wire is made smaller or its length 

Resistance increases With increased length of wire; or 

As diameter is decreased; or 

As the temperature is increased above 

normal; or 
As the composition of the wire is 

changed to an alloy having lower 


Resistance decreases As length of wire is decreased; or 

As the diameter is increased. 

As the temperature is reduced, if it be 

above normal. 

As the composition of the wire is 
changed to an alloy having higher 

NOTE. The difference in conductivity of different metals makes the 
analogy of water and current action more complete, since it corre- 
sponds to roughness or smoothness of walls of the water pipe. 

Different metals offer varying resistance to electric current as 
follows, taking the resistance of pure silver and pure copper as 1. 

Copper 1 *18% German Silver 19 

Silver 1 Manganin 24 

Aluminum 1.5 *30% German Silver 28 

Platinum 6 *Advance Wire 28 

Norway Iron 7 *Climax Wire 50 

Soft Steel 8 *Nichrome 60 

*Ferro Nickel 17 

NOTE. The Driver-Harris Company, manufacturers of resistance 

wires, are authority for these figures. I know of no more reliable 

source for information of this kind. Star (*) indicates Driver-Harris 

In the foregoing table the figures refer to the amount of 
resistance each metal has, as compared to that of pure, an- 
nealed copper. For instance, platinum has 6 and climax wire 
50 times the resistance of pure, annealed copper. 

I have selected for a part of this table metals and composi- 
tions in very general use for resistance purposes. It will, of 
course, be understood that the figures given in the tables are 
based on metals and alloys of a certain standard purity, but 
inasmuch as the degree of purity will, in the very nature of 


things, vary to some extent, the figures cannot be relied upon 
for absolute accuracy. 

It must also be understood that the resistance of nearly all 
metals increases with rise of temperature, whereas the resist- 
ance of carbon decreases as its temperature increases. The 
resistance of the carbon filament of the incandescent lamp of 
the ordinary type is about twice as much when cold as when 
burning at candle power. As a general proposition the re- 
sistance of liquids and insulating materials become less with 
increased temperature. 


The resistance of a wire is not constant at all temperatures. 
If you increase the temperature of a metallic wire you also 
increase its resistance, and this increase in resistance follows 
a definite law, viz.: 

In metals increase or decrease in resistance is directly in pro- 
portion to increase or decrease in temperature. 

The factor that will enable you to calculate this increase or 
decrease, provided you know the difference in temperature, 
is called the "temperature coefficient." In all catalogs of re- 
sistance wire the resistance per foot of the material is given 
at a certain standard temperature, usually 75 degrees F, and 
the resistance at this standard temperature will form the 
basis for calculation of increased or decreased resistance by 
reason of temperature change. The figure given for tem- 
perature coefficient is the fraction of an ohm change in re- 
sistance for each degree F change in temperature, and this 
coefficient must be multiplied by the number of degrees of 
the temperature change from the standard 75 degrees, and 
the result added to or subtracted from the standard resistance, 
depending upon whether the material increases in resistance 
with heat as metal does, or decreasing with heat as some 
other substances, carbon, for instance, do. For example, let 
us assume the temperature coefficient of a given material to 
be .001 per degree F., and that its resistance at 75 degrees F. 
is 10 ohms. What will be its resistance at 175 degrees.? 

Subtracting 75 from 175 we find the difference in tempera- 
ture to be 100 degrees. If the resistance increases .001 of 
an ohm for each degree of increased temperature then for 
100 degrees increase of temperature the increase of resistance 
would be .001X100 = .!. Now, multiply the resistance (10 
ohms) at 75 degrees by the fractional increase, which is .1, 


which gives us the actual total increase of 10 X .1 = 1 ohm, so 
that the resistance at 175 degrees F will be 10 ohms, the 
standard resistance, plus 1 ohm increase, or a total of 11 ohms. 


Electric conductors are ordinarily selected with one of two 
ends in view. In one case low resistance, tensile strength, 
ductility, and cost are the ruling factors; in the other case 
comparatively high and steady resistance is the important 

In the first instance conductors for current distribution is 
the thing considered, and, by reason of the fact that it more 
nearly combines the four above-named important factors than 
any other metal, copper has been selected as the standard 
electrical conductor, an office which it shares only, to some 
slight extent, with aluminum, the latter being used in a few 
instances for high tension lines. 

In the second instance a material to offer resistance is the 
thing desired, and for a long time the metal used almost ex- 
clusively for this purpose was German silver. Gradually, 
however, German silver has been largely displaced, until it is 
now but little used except in alloy combinations with other 

The materials now most generally used for resistance in 
motion picture projector circuits are either cast iron, made 
up in grid form, or some one of the nickel-steel resistance 
wires. Reliable data concerning the properties of cast iron is 
difficult, in fact practically impossible to obtain, but it may be 
said that it forms an excellent and cheap resistance medium 
where considerable variation at different temperature is not 
of great importance. 

Properties of Resistance Metals. "Normal" is 75 F. or 24 
C. The resistance per mill-foot of pure nickel is 64.3 ohms 
at normal. Climax resistance wire, made by the Driver- 
Harris Company, Harrison, N. J., has a resistance per mill- 
foot of 525 ohms at normal; its temperature coefficient is .0004 
per degree F. It is a nickel steel alloy with a resistance fifty 
times that of copper. This metal is excellent for rheostat 

German silver is a composition containing 18 per cent, of 
nickel. It is known as "18 per cent. German silver." Its re- 
sistance varies somewhat with different lots. Its mill-foot 
resistance is 218 ohms at normal; its temperature coefficient 
.00017 per degree F. 


Ferro nickel has a mill-foot resistance of 170 ohms at 
normal; temperature coefficient is .00115 per degree F. 

Yankee silver is a new alloy, put out by the Driver-Harris 
firm, which is claimed to be an improvement on the 18 per 
cent. German silver in that it withstands rapid heating and 
cooling well, and gives good service where German silver 
fails. Its resistance is 200 ohms per mill-foot; its tempera- 
ture coefficient is very low, being .000086 per degree F. 

Nichrome, also a Driver-Harris product, is a practically 
non-corrosive alloy with high melting point about 2600 de- 
grees F. It is designed for use where high temperatures are 
the rule, such as heating coils, etc. Its mill-foot resistance 
is 600 ohms; its temperature coefficient .00024 per degree F. 

Advance wire, a Driver-Harris product, is a copper-nickel 
alloy containing no zinc. It is claimed to be constant in its 
resistance under all conditions of service; therefore it has no 
temperature coefficient. Resistance per mill-foot is 294 ohms. 
It is particularly recommended for electrical instruments 
where the resistance is subjected to repeated heating and 


It is highly desirable and under certain conditions very 
necessary that the operator be able to figure the resistance 
of the various circuits in the theatre or of the feed-wires lead- 
ing thereto. As has already been pointed out, the overcoming 
of resistance consumes voltage. All wires offer resistance 
to current, and voltage will be consumed in (a) proportion to 
the size of the wire; (b) the length of the wire; (c) the 
amount of current flowing; (d) composition of the wire. 

Up to a certain point the resistance of the wire remains 
without change; that is to say, the resistance offered to one 
ampere or ten amperes will be identical, but when the load 
becomes such that the temperature of the wire begins to rise, 
then the resistance also begins to rise, and the effect is, as 
has already, been explained, a loss in voltage, with the result 
that the lamps will not burn to candle power and the meter 
is registering wattage which is being wasted in overcoming 
the excessive resistance of the wires. 

Copper wire used for electric current can carry a certain 
number of amperes without causing any appreciable rise in 
temperature, and the National Board of Fire Underwriters, 
which is the controlling factor, has adopted the amperage 
rating recommended by the American Institute of Electrical 
Engineers. This determines the number of amperes which 


any wire may be allowed to carry, which are set forth in 
Table No. 1, in which "B. & S." means "Brown & Sharpe 
Wire Gauge." For reasons why more current is allowed on 
weather-proof than on rubber-covered see "Insulation," page 50. 


Rubber Other 

Insulation Insulations Circular 

B. & S. Amperes Amperes Mills 

18 3 5 1,624 

16 6 10 2,583 

14 15 20 4,107 

12 20 25 6,530 

10 25 30 10,380 

8 35 50 16,510 

6 50 70 26,250 

5 55 80 33,088 

4 70 90 41,740 

3 80 100 52,630 

2 90 125 66,370 

1 100 150 83,690 

125 200 105,500 

00 IsO 225 133,100 

000 175 275 167,800 

0000 225 325 211,600 

For insulated aluminum allow 84 per cent, of above table 

ratings. The Board of Fire Underwriters does not recognize 

anything of less size than No. 18 wire, and nothing less than 

No. 14 can be used for interior circuit wires. 

The figuring of the resistance of a wire of any size or 
length is a simple matter, provided the standard of resistance 
for that particular material be known. 


The accepted standard of resistance is the resistance of a 
wire one circular mill in cross-section (one one-thousandth of 
an inch in diameter) and one foot in length, made of the 
same material as the wire it is proposed to measure. This is 
what is known as the "Mill-foot standard of resistance." The 
resistance of such a wire, when made of ordinary commercial 
copper, is given by standard text books as 10.5 ohms. That 
is to say, a wire one foot in length and one one-thousandth 
of an inch in diameter (one mill cross-section), made of 
ordinary commercial copper, at normal temperature (75 F. or 
24 C), will have a resistance of 10.5 ohms. 





Resistance at 75 F., International Units 





6 . 




Ohms per Lb. 




1000 Feet 














































































* 5.340 



























































































































































And now let us proceed to apply the foot-mill standard in 
measuring wires. Suppose you have a wire 400 feet in length 
and 1 mill-foot in cross-section (1/1000 of an inch in diameter) 
made of ordinary commercial copper. It is evident that if 
one foot of such a wire has a resistance of 10.5 ohms, 400 
feet would have a resistance four hundred times as great, or 
10.5X400 = 4200 ohms. The resistance of a wire of given 
length, however, decreases, as its diameter, area or cross-sec- 
tion is increased. Now if our 400-foot wire has a diameter 
of 250 mills it will have a cross-section equal to 250 X 250 = 
62,500 C. M., and it follows that its resistance would be equal 
to the resistance of 400 feet of one-mill wire (4,200 ohms) 
divided by the C. M., cross-section of the larger wire (62,500), 
since it would be, in effect, equal to 62,500 wires, each one 
circular mill in cross-section, or one mill in diameter. From 
this we get the rule: 

To find the resistance of a copper wire, multiply its length in 
feet by 10.5 and divide that product by its area in circular mills. 

In measuring circuits, however, it is customary to take the one 
way length and double the mill-foot standard, thus: multiply the 
one way length of the circuit by 21 (10.5X2 = 21) and divide 
that product by the area of the wire in the circuit; expressed 
in circular mills. 

For example: What is the resistance of a two-wire oper- 
ating room feed circuit 300 feet in length size of the wire 
No. 5? Now if we were just measuring one 300-foot-long wire 
we would apply the above rule, using 10.5 as the standard of 
resistance, but as a matter of fact a circuit 300 feet long has 
600 feet of wire, and, for convenience sake, we double the 
mill-foot standard, instead of doubling the wire length. 

In Table 1, page 42, we find that No. 5 wire has a cross- 
section of 33,088 C. M. We then .have the problem: 
Length of circuit X 21 300 X 21 

= = 1874, or say .2 of an ohm, 

Area of wire 33,088 

which is the resistance of the circuit. This rule is, of course, 
based on the proposition that the wire will not exceed 75 
degrees F., or 24 degrees C. However, the rise and fall in 
temperature caused by ordinary climatic conditions is not 
sufficient to effect the result materially. In fact, resistance 
does not begin to rise appreciably until the temperature has 
increased sufficiently to be sensible to the feeling; beyond 
that point it increases very rapidly with the temperature. 


The foregoing is good for any number of amperes up to the 
capacity of the wire, or, in other words, until the load becomes 
great enough to cause a distinct rise in temperature. For 
instance: If you propose to carry only 5 amperes on a No. 5 
wire you would have exactly the same total resistance you 
would have if you pulled 50. 

Theoretically this is not strictly true, since there is a rise 
in temperature with any increase in current, but it is true in prac- 
tice, nevertheless, by reason of -the fact that with any load 
less than the wire's capacity the temperature rise is too slight 
to have appreciable effect. 

When figuring copper wire resistance still another equation 
enters, however, and a very important one, too, viz., drop in 


It has been laid down as a general rule that: 

For the transmission of any given amperage the most econom- 
ical condition is one where the line resistance is of such value that 
the value of the energy wasted in heat in overcoming the resist- 
ance of the line will be equal to the interest per annum on the 
original cost of the conductor. 

The question of drop in voltage in theatre circuits is usually 
given too little consideration. Where the length of the cir- 
cuit, the cross-section, or area of the wire, together with its 
mill-foot standard of resistance, is known, the ohmic resist- 
ance may be calculated according to: 

21 XL 

Formula No. 1: R = 


in which R is resistance in ohms; L the one-way length of the 
circuit, expressed in feet; A the cross-section, or area of the 
wire in circular mills, and 21 a constant equal to twice the re- 
sistance of the mill-foot standard for copper wire. Twenty- 
one and the one-way length of the circuit are used, instead of 
10.5 and the total length of the two wires, merely for the 
sake of convenience. 

Formula No 2: e = IXR 

in which e is the voltage drop; I the current in amperes, and 
R the resistance of the circuit. 

21 X I X L 

Formula No. 3: e = in volts. 


21 X I X L 
Formula No. 4: A = in circular mills. 

Formula No. 5: 1 = in amperes 

Formula No. 6: L = in feet. 


When it is required to give a working formula for a given 
number of lamps expressed by N, each of which requires am- 
peres represented by I, use Formula No. 7. 

21 X N X I X L 
Formula No. 7 : A = area in circular mills. 

When the drop is expressed as a percentage, the size of the 
wire may be determined by Formula No. 8. 

2100 X I XL 
Formula No. 8: A = area in circular mills, E 


being the voltage of the circuit and P the percentage drop. 

Where, as is often the case, the power, W, is given in watts 
instead of amperes, use Formula No. 9. 

2100 X WXL 
Formula No. 9: A = area in circular mills. 


If it is desired to find the number of lamps to which a given 
size of wire will supply current with a given drop use For- 
mula No. 10. 


Formula No. 10: N = 

21 X L X I 

Applying formula No. 2, let us assume a current of 100 
amperes in a circuit whose resistance figures .02 of an ohm. 
Multiplying 100 amperes by .02 we get 2 volts as the drop in 
that circuit. Formulas Nos. 3, 4, 5, 6, 7, 8, 9, and 10 are ob- 
tained by substituting the value of R in Formula No. 2 for R 
in Formula No. 1. Also for convenience L (length of circuit) 


is made equal to 2L, so that only the distance one way need 
be considered. 

And now let us assume an example. A two-wire operating 
room feeder supplies 50 amperes at a distance of 200 feet from 
the house switchboard; the drop allowed is 5 per cent, the 
voltage 110. What size wire should be used? Referring to 
the formula, we select No. 8, and, substituting figures, the 
necessary size of wire is found as follows: 

2100 X 50 X 200 

A = 38181 circular mills. 

110 X. 05 

Turning to our capacity table we find that a No. 4 wire has 
an area of 41738 CM. and a No. 3 has 52624, so that a No. 3 
would be largely in excess of the requirements and a No. 4 
would be too small. 

If this energy were used for ten hours a day for 300 days 
and the cost of the energy were 8 cents per k.w. hours, the 
total yearly cost would be: 

50 X HO X 300 X .08 

== $1,320 


five per cent, of which is $66, which latter amount would ex- 
press a yearly loss due to the 5 per cent, drop when using 50 
amperes at 110 volts. The cost of 400 feet of No. 4 wire would 
be about $21, hence the yearly loss would be more than three 
times the cost of the wire, and, without further calculation, 
it is very readily seen that No. 4 wire would not be econom- 
ical for this service. If, on the other hand, wires sufficiently 
large to only cause a four per cent, loss be used, it is no 
difficult matter to figure out the saving and discover the 
fact that it would considerably more than pay interest on 
the added copper cost with current at 8 cents per kilo- 
watt. Suppose, however, the price of electricity were 6 cents 
per k.w. instead of 8. The installation of such a large cable 
would then not be profitable, since the saving would be less, 
hence, less investment in copper would be necessary. 

This data is of much importance to both operator and man- 
ager, because by the use of the B. & S. wire gauge and a tape 
line they will be able to figure out the approximate loss in 
their various circuits, and in many instances it will be found 
that they are paying heavily for energy wasted in line resist- 
ance. There .are many operating room feed circuits that are 
giving a 5 per cent, drop, or even larger than that, and all this 


waste energy is registered on the wattmeter. Therefore, I 
repeat, it is essential that the operator and manager have a 
good working knowledge of questions of this kind. 

Note: In the foregoing I neglected to include increase of 
cost for installing larger wires. This must be added to initial 
cost of wire in order to arrive at the correct result. 

Further data on resistance as applied to the projection lamp 
arc circuit will be found under the head, "Resistance Devices." 

Measuring Wires 

LECTRIC conductors of various kinds are measured as 
to their cross-section or area in square and circular 
mills, circular mills being used for round wires and 
square mills for square or rectangular conductors. 

A square measuring 1/1000 of an inch on each of its four sides 
is called a "square mill.'* A circle 1/1000 of an inch in diameter 
is called a "circular mill," commonly designated "CM." 

A round wire 1/1000 of an inch in diameter is said to have 
an area of cross-section of one circular mill. 

The areas of all round wires are directly proportioned to the 
square of their diameters, the calculation being made in mills 
(thousandths of an inch). 

"Squaring the diameter" means multiplying the diameter by 

It therefore follows, if the areas of the circles are propor- 
tional to the squares of their diameters, and the area of a wire 
one mill in diameter is called one mill, or one "circular mill" 
(C.M.), then wires of other sizes have an area of cross- 
section, numerically equal, in circular mills, to their diameter 
in one one-thousandths of an inch (mills) squared, or multi- 
plied by itself, thus: If a wire be 10 mills in diameter, then 
100 (10 X 10) is the "square" of its diameter, hence its area of 
cross-section in CM. 

Let us also consider a wire one-quarter of an inch in diam- 
eter. Since the wire is one-quarter inch in diameter, and one 
inch is equal to 1000/1000, then the diameter of the wire ex- 
pressed in thousandths of an inch, or mills, would be equal 
to 1000-^4 = 250. Such a wire would then be 250/1000 of an 
inch in diameter, or, expressed otherwise, 250 mills in diam- 
eter. And since the area of cross-section of a wire in circular 
mills is equal to its diameter in mills multiplied by itself 
(squared), it follows that the area of the wire in question 
would be 250 X 250 = 62,500 circular mills. 



The circular mill area of any round wire may be found by meas- 
uring its diameter in thousandths of an inch, using a micrometer 
caliper or wire gauge for the purpose, and multiplying the meas- 
urement thus obtained by itself. 

There are several methods of measuring wires. The ac- 
cepted standard for wire measurement in this country is the 
American Gauge, commonly known as the "Brown & Sharpe 
Gauge," and in practice dubbed the "B. & S." gauge, the same 
being illustrated in Fig. 7. 

In using this tool it is the slot and not the round hole that de- 
termines the size of the wire, and while the wire must not 
actually bind in the slot, it must fit snugly. The gauge, if it 

Figure 7. 

be a good one, will have the width of each slot, or, in other 
words, the diameter of the wire which fits the slot, stamped 
opposite each slot on one side of the gauge, and the number 
of the wire stamped opposite the slot on the other. In Fig. 7 
it is the wire number side we see. The diameter in thousandths 
of an inch is the same thing as the diameter in mills. For 
instance, No. 16 wire has a diameter of fifty-one thousandths 
of an inch, or, in other words, 51 mills, the term thousandths 
of an inch and mills being interchangeable. 

One of the most convenient and at the same time most 
accurate methods of measuring wire is by means of a mi- 
crometer caliper. See Fig. 8. These calipers may now be 
had with the wire size and their equivalents in mills (thou- 


sandths of an inch) stamped thereon. For instance, in the 
illustration we see "4/0," with 460.0 opposite it, which means 
that 0000 (called "four 0") wire is 460 mills (460 thousandths 
of an inch) in diameter. These tools are expensive, but, on 
the other hand, they are mighty good articles to own, and 
ought to be included, in one form or another, in every oper- 
ator's tool kit. 

Figure 8. 

For measuring very small wires, such as the strands of an 
asbestos-covered wire (usually No. 30 or 31), the slot wire 
gauge is not very reliable except in the hands of an expert. 
If you have no micrometer caliper it is better to have a 
machinist make the measurement for you with his. Have 
measurements made of three or four strands from different 
parts of the wire. 

For most purposes, however, the wire gauge, in conjunction 
with the wire capacity table, page 42, will answer all purposes. 


WHEN there is a difference in potential maintained 
between two wires of an electric circuit these wires 
have an affinity for each other and current seeks 
constantly to pass from one to the other. The purpose of 
insulation is to prevent this and to keep the wires from 
coming into electrical contact with any object which might 
furnish an electrical path to a wire of opposite polarity at- 
tached to the same dynamo. Such a path may be found 
through the ground or through any current-carrying material 
having electrical contact with wires of opposite polarity. 
In short, insulation is to protect the potential of or on a 
wire interference by any outside source. 


As we have already seen (page 38), various metals offer 
varying resistance to the passage of electric current. Not 
only is this true, but various materials other than metals 
offer varying resistance to the passage of electric current, 
and, while there is no material which is a non-conductor 
that is to say, through which electric current cannot be 
forced if the pressure (voltage) be raised sufficiently high, 
still there are materials which are considered! and treated 
as non-conductors, because no ordinary voltage will force 
current through them. These substances are called "insulat- 
ing materials," at the head of which stand, in the order 
named, glass, procelain, and rubber. Various natural sub- 
stances such as marble and slate form excellent insulating 
materials, and asbestos, when dry, is also a very good in- 
sulator. There are also various insulating compounds, the 
composition of which are trade secrets. In practice these 
compounds are used to saturate some kind of braided or 
other material which, after being so saturated, is used for 
weatherproof insulation on wires to be used out of doors, or 
to reinforce the rubber insulation of rubber covered wires. 

Procelain is, for the most part, used to line holes in brick 
or other walls through which it is necessary to pass wires 
and for knobs to carry wires which are run in open circuit 
through the air, or along walls. Rubber, on the other hand, 
is, for the most part, used for inner insulation of what is 
called "rubber covered" insulation of wires. Glass is used 
only for pole insulators on low potential, owing to its fragile 

Rubber covered wire consists of tinned copper wire with 
a covering of rubber or rubber compound of homogeneous 
character, reinforced by an outer covering of braided cotton 
soaked in preservative insulating compound. Where copper 
wire is covered with any of the rubber compounds the tin- 
ning of the wire is very necessary, since the sulphur uni- 
versally present in rubber insulation is likely to combine 
with the copper and in a short time the wire would be cor- 
roded, and either very greatly weakened or, if a small wire, 
entirely destroyed. The tinning of the wire prevents thij, 
since tin will not combine with sulphur and the rubber in- 
sulation has no effect upon it. 

It is not, however, the purpose of this book to go into an 
exhaustive treatise on insulation materials, but merely to give 
the operator a general understanding of the proposition. 

The current must be confined to the wire and made to pass 
from the positive to the negative through the paths provided, 


and through them only, the said paths being motors, in- 
candescent globes, arc lamps, etc. The strength of insulation 
must increase with the potential, and its kind may vary with 
the service. For instance: the insulation known as "weather- 
proof" may be used where the wires are stretched in open 
air on out-door circuits. On the other hand, for interior 
work while this same insulation may still be used, under- 
neath it and next the wire there must be a coating of pure 
rubber or rubber compound. The insulation then becomes 
what is known as "rubber covered." Its disadvantage lies 
in the fact that rubber deteriorates rapidly under the influence 
of even moderate heat, and is immediately destroyed by any- 
thing like high temperature. The necessary strength of the 
insulation, either weatherproof or rubber covered, will depend 
upon the voltage. 

There are several ways of testing the insulation of wires, 
the test here given being that required by the National 
Board of Fire Underwriters for rubber covered wire. 


Any one-foot sample of completed covering must show a 
dielectric (dielectric is defined as any substance or medium 
that transmits the electric force by a process different from 
conduction, as in the phenomena of induction; a non-con- 
ductor separating a body electrified by induction from the 
electrifying body) strength sufficient to resist, for a period of 
five minutes, the application of voltage proportionate to the 
thickness of the insulation, in accordance with the following 


Breakdown test on 1 foot 
Thickness in 64th inches Volts A. C. 

1 3000 

2 6000 

3 9000 

4 11000 

5 13000 

6 15000 

7 16500 

8 18000 
10 21000 
12 23500 
14 26000 
16 28000 


In making the foregoing test the source of electro-motive 
force (voltage) must be a transformer of at least one kilowatt 
capacity. The application of the electro-motive force shall 
be made at 3000 volts for five minutes, and then the voltage 
must be increased by steps of not more than 3000 volts each, 
the voltage of each step being held for five minutes until 
the maximum for a given thickness of insulation is had, or 
until there is a rupture of the insulation. The test for die- 
lectric strength must be made on wire which has been 
immersed in water for seventy-two hours, one foot of the 
wire under test to be submerged in a conducting liquid held 
in a metal trough, one of the transformer terminals being 
connected to the copper of the wire, and the other to the 
metal of the trough. 

There are two types of weather-proof wire, viz.: weather- 
proof and slow-burning weather-proof. The insulation of 
the slow-burning weather-proof consists of two coatings, one 
of which is fire-proof in character, while the other is 
not. The fire-proof coating is on the outside and com- 
prises about six-tenths of the total thickness of the insula- 
tion. The complete covering for sizes of wire from No. 14 
to No. 0000 varies from 3/64 to 5/64 of an inch. The fire- 
proof insulation is not as susceptible to fire as is ordinary 
weather-proof, nor does it as readily soften under the influ- 
ence of heat. It is not suitable, however, for outside work, 
being intended for interior work in dry, warm places such as 
shops and factories. There is another type of wire insulation 
called "slow-burning," which is still more fire-proof than is 
the slow-burning weather-proof. It is intended to be used 
in very hot places where ordinary insulation would soon per- 
ish. The insulation of weather-proof wire should consist 
of at least three layers of braid, each of which is thoroughly 
saturated with a dense, moisture-prool; compound, applied 
in such manner as to drive any atmospheric moisture out of 
the cotton braiding, thereby securing a covering to a great 
degree water-proof and of high insulating power. The outer 
surface of this insulation is pressed down to a hard, dense 
surface. This wire is for use out of doors where moisture 
is certain and where fire-proof qualities are not necessary. 
In general, weather-proof wires can be used only where the 
insulating supports on which the wire is mounted are de- 
pended on for insulation, the covering being regarded simply 
as a precaution against accidental contact with other wires or 
other objects. 


From the foregoing it will readily be understood that the 
principal difference between rubber-covered and other in- 
sulation lies in the fact that the rubber-covered insulation 
may be depended upon entirely for insulating, whereas the 
others must depend, at least to a considerable extent, on the 
insulating supports for their insulation. Rubber-covered wire 
may be used in any place that weather-proof would be allow- 
able, but not in places where slow-burning insulation would 
be required. Double braid rubber-covered wire is the only kind 
that may be used in conduits, where the two wires of the circuit 
lie side by side. So far as the carrying capacity of copper be 
concerned it makes absolutely no difference what the insula- 
tion be composed of. The reason that rubber-covered wire 
is rated at lower capacity than weather-proof is by reason 
of the fact that rubber is easily injured by even moderate 
heat, hence when it is used a high margin of safety is main- 

Under no circumstances is it permissible to use other than 
wire having rubber-covered insulation inside of conduits. 

Wire Systems 

IT is highly desirable that the operator have a good work- 
ing knowledge of the various wire systems with which 
he is likely to come in contact. It is not the purpose of 
this work to make the operator a wireman, or an electrician 
for that matter, but merely to give him a fairly comprehen- 
sive general idea of the action of electric current and the 
appliances, including the wire systems, with which he will 
have to do. 

On the road, particularly when playing small towns, the 
operator may be called upon to connect to any one of the 
several different wire systems, and unless posessed of knowl- 
edge he will be unable to proceed with any degree of certainty 
or confidence. 

There is one wire system with which it is impractical I 
might even say impossible to connect a projection arc, 
viz, the series arc system. This system is used only for 
street arc lighting. Instead of two wires it only has one, and 
each lamp carries the entire amperage of the system, or 
circuit. The voltage of the series arc system will depend upon 
the number of lamps, there being an added pressure of about 
50 volts for each lamp, so that a circuit supplying ten lamps 
would have a pressure or voltage of 50 X 10 = 500 volts, whereas 
if there were eleven lamps the pressure would be SOX 11=550, 



and so on. Do not attempt to connect your projection 
lamp to the series arc system, because if you do you will 
fail; also you will cause serious trouble, and may succeed 
in getting yourself badly shocked, or possibly even killed. 
Fig. 9 is a diagrammatic representation of a 10 lamp series 
arc system. 

? : 

<p <j? 

rh rh 

T -^~ 


M^ T 

Figure 9. 

There was at one time a system called the "series-mul- 
tiple" and another called the "multiple-series," but with these 
it is unnecessary, I think, to deal, since they have been 
practically if not entirely abandoned. 


The "multiple arc system," also called the "two-Jwire 
system," is, to all intents and purposes, the only one with 
which the operator comes into contact, the three-wire system 
being but a variation of the two-wire system, so far as elec- 
trical action and practical effect be concerned. 

Figure 10. 

In Fig. 10 we see diagrammatic representation of what is 
varyingly styled the "multiple arc," "parallel" and "two- 
wire" system. The heavy lines represent mains coming from 


the power house, the less heavy ones, D-D, branch mains 
feeding a district or street, and the thin lines, E-E-E, house, 
store, theatre circuits, etc. In theory the current flows out 
from the dynamo on the positive wire, through the various 
lamps, etc., to the negative, and back on it to the dynamo. 

In one of the house circuits a projection lamp is attached, 
all switches, fuses, etc., being omitted for convenience. As- 
suming that the system carries not more than 500 volts we 
may attach a projection lamp to the wires at any point, 
provided (a) the wires, switches, etc., be large enough to 
carry the current necessary for the arc, plus whatever else 
they will have to carry, without overload; (b) the fuses be 
large enough to carry current for the arc, plus whatever 
else it will have to carry; (d) provided sufficient resistance 
be connected in series with the lamp to reduce the line 
voltage to arc voltage. 

If the system be D. C. the voltage will not, in any event, 
exceed 500, and, except in the case of power lines for street 
car service, seldom goes above 22. 

If the current be alternating then you can attach your pro- 
jection lamp at any point, provided the same precautions be 
taken as before named for D. C., but if the line be what is 
called high tension (1000 volts or more), then you can only attach 
your projection lamp on the secondary side of a transformer. 
In this connection the traveling operator should always have 
a copy of McGraw's Electrical Directory, which is for sale 
by McGraw Publishing Company, 239 West Thirty-ninth Street, 
New York City, costs $10 a year, and gives particulars of every 
light plant in the country. If he is not the possessor of this book, 
then the first thing for him to do upon entering a town is to 
call up the power house and ask: (a) the kind of system; 
(b) voltage of the system; (c) if the show is to be given in a 
church, school house, or hall, and the current is A. C., and 
whether or not the transformer supplying the building in 
which the show is to be given is large enough to supply the 
projection arc,- plus whatever else it has to supply. 


The three-wire system is a very popular and widely used 
method of electric light and power distribution. Its basic 
principle is the fact that if two batteries or two generators, 
of the same voltage, be connected in series with each other, 
the voltage between the positive terminal of one generator 



or battery and the negative terminal of the other generator 
or battery will be double the voltage of either battery or 
dynamo separately. Thus if each dynamo be a 110 volt 
generator, then the voltage between the positive of one 
machine and the negative of the other would be 220 volts, 
but if, at the same time, the voltage be taken across the 
positive and negative brush of either machine separately, 
the reading will be only 110, or whatever the voltage of the 
individual machines may be. It therefore follows that if a 
wire be attached to the positive of one generator and the 
negative of the other generator, the voltage between these 
two wires will be double the voltage of either generator 
taken separately, and if a third wire be attached to the 
jumper connecting the two generators the voltage between 
either of the outside wires and the center wire (called the 
"neutral") will only be the voltage of the individual dynamo, 
or half the pressure between the two outside wires. 



Figure 11. 

In Fig. 11 A and B are 110 volt generators; C is a jumper 
connecting the negative terminal of machine A with the 
positive terminal of machine B; D is a wire attached to 
jumper C, the same being called the "neutral" wire: E is a 
wire attached to the positive terminal of generator A; F is a 
wire attached to the negative terminal of generator B; G is a 
voltmeter attached between wires E and D; H is another volt- 
meter attached between D and F, and I is a third voltmeter 
attached between wires E and F. Assuming generators 
A and B to be 110 volt machines then voltmeters G and H 
will each read 110, whereas voltmeter I will read 220. If 


generators A and B were each 70 volt machines, then volt- 
meters G and H would each read 70, whereas voltmeter 1 
would read 140. Still referring to Fig. 11, J, K, L, M, and N 
are ordinary 16 c.p. incandescent globes, requiring, let us 
assume, half an ampere of current each. 

The electrical action is as follows: For the moment 
switching off globes J, L and N let us consider only lamps 
K and M. Under this condition a half ampere of current at 
220 volts pressure would pass out from the positive brush of 
generator A, along wire E to lamp K, which is a 110 volt 
lamp, as is also lamp M, therefore the combined resistance 
of the two lamp filaments will be just sufficient to allow a 
half ampere of current to flow. Thus a half ampere passes 
through lamp K, into the neutral wire and back toward the 
generator, but instead of traveling on and into jumper C, 
it switches off, goes through lamp M and thence back on 
wire F to the negative terminal of generator B. In other 
words, lamps K and M burn in series with each other, and 
under this condition no current at all passes over the neutral 
wire between lamp M and jumper C. 

Now, taking a step further, let us consider J, K and L. 
Each lamp requires, let us assume, 55 watts; therefore, 55 X 
3 = 165 watts, divided by 110=: \y 2 amperes passes out on 
wire E, through the lamps, into the neutral and starts back 
thereon, but 55 watts (^ ampere) passes through lamp M, 
and another 55 watts ( l /2 ampere) passes through lamp N 
into wire F, which accounts for one ampere, and leaves 55 
watts ( l /2 ampere) yet to be accounted for, which must pass 
back to the negative terminal of generator A, over the neu- 
tral wire, D, so that under this condition (called an "un- 
balanced system") we have \ l / 2 .amperes flowing on wire 
E, 1 ampere on wire F, and l / 2 ampere on wire D. For the 
sake of added clearness I have mapped out the course of the 
current with arrows which indicate the current flow. 

In figuring the amperage of a 110-220 volt three-wire system 
remember this: 

If you have 110 volt lamps or motors on one side rated 
at a given number of amperes you can add 110 volt apparatus 
of equal capacity on the other side without increasing the 
number of amperes flowing in the system. The electrical 
effect is the same as though you removed the 110 volt ap- 
paratus from the first side and substituted 220 volt apparatus 
of double h. p., connected between the two outside wires. 

With a three-wire 110-220 volt system either 110 volt or 
220 volt apparatus may be used. If you connect a motor or 


lamp from either outside wire to the neutral it must be a 
110 volt motor or lamp; if you connect a motor or lamp 
from outside to outside wire it must be a 220 volt motor or 
lamp, always assuming the generators to be 110 volt ma- 
chines, as they are in practically all cases. 

The ideal condition with a three-wire system presumes it 
to be perfectly "balanced," meaning by this that 110 volt 
apparatus (motors and lamps) drawing the same total am- 
perage be connected to both sides. If in a light and power 
system there is 110 volt apparatus connected to one side, 
wires E and D, Fig. 11, drawing a total of 240 amperes, then 
there should be 110 volt apparatus connected to the other 
side, wires D and F, Fig. 11, sufficient to use 240 amperes. 
Under this condition the system would be perfectly bal- 
anced, and all apparatus would work in series, so that, so far 
as the actual operation of the lamps and motors be con- 
cerned, the neutral wire might be disconnected from the 
dynamo entirely. In other words, if the neutral fuse at the 
power house blew, or was removed, there would be no effect 
at all. The total amperes would only be 240. 

This ideal condition is, however, seldom or never real- 
ized in practice. There is practically always more load on 
one side than on the other, and amperage equal to the dif- 
ference between the load on the two sides flows back to the 
generator on the neutral wire. If there are 26400 watts 
being used on one side and 24200 on the other, then 26400 
24200 = 2200 -M 10 = 20 amperes would flow back to the gen- 
erator on the neutral wire, and the practical effect would be 
that one generator would be producing 20 amperes more 
than the other. 

It is for this very excellent reason that heavily loaded systems 
often object to projection arcs being connected to one side 
of the system. Both dynamos are working up to their 
capacity, and if a projection arc pulling, say, 40 amperes 
be hitched to one side its load is all thrown on one dynamo 
and the system is thus unbalanced. However, if the opera- 
tor is reducing his voltage with a rheostat it would not help 
matters in the least to connect across the outside wires, 
since, although- the amperage would remain the same the 
generators must put out double the amount of energy, and 
instead of having one dynamo loaded that much heavier, 
we have both carrying an additional load equal to amperage 
times 220, one-half of which is carried by each generator, 
which represents pure, unadulterated waste. If an economizer, 
a mercury arc rectifier, or a motor generator set be used, 



however, then it is different, since the total energy taken 
from the lines will be practically the same when connected 
across on 220 as it would on one (110 volt) side. 

It may be said that, as a matter of fact, if you use a rheo- 
stat for resistance the power company can have no reasonable 
excuse for compelling you to attach your projection arc to the 
outside wires of a three-wire system. It simply costs you that 
much more, and does not relieve the power plant in the 
least; in fact it adds to the total load. 

The operator encounters some very puzzling questions in 
connection with the three-wire system. For instance. 



Figure 12. 

In Fig. 12 we see a three-wire system fused at 60 amperes. 
From these lines are taken six circuits A, B, C, D, E, and F, 
five of which have apparatus attached to them requiring 10 
amperes of current each. Now with those 60 ampere fuses 
would it be possible to attach a 25 ampere projection arc 
to the idle circuit F? At first glance you may say No; you 
are already pulling 50 amperes, since 5 X 10 makes 50, and 
right there you make a mistake, because you are not doing 
anything of the sort. You are pulling a total of 20 amperes 
across the outside wires, and 10 additional amperes on one 
side, so that fuse 1 carries 30, fuse 2 10 and fuse 3 20 amperes, 
therefore on the side that the idle circuit is on you are only 
pulling 20 amperes, and if you attach a 25 ampere arc you 
will still have a leeway of 15 amperes. Why? 


The answer is simple. It is purely a question of wattage. 
One side has 110 volt apparatus requiring a total of 20 X HO 
= 2200 watts. The other side requires 30 X HO = 3300 watts. 
The current comes out on wire 1, at 220 volts pressure. It 
is forced through the 110 volt motor and lamps, 110 volts 
of the pressure being consumed in so doing. It is then on 
the neutral wire, still 30 amperes, but at 110 volts pressure; 
therefore it still has power equal to 110X30 = 3300 watts. 
Now the neutral is negative to wire 1 but positive to wire 3, 
and wire 3 is the TRUE negative of the combination. Therefore, 
there is still the inclination to seek the negative (true negative), 
but the apparatus connecting wires 2 and 3 only requires 
110X20 = 2200 watts, so that when they have been supplied 
10 amperes 10X110=1100 watts remain, and, being unable 
to reach the true negative, wire 3, must pass back to the 
generator on wire 2, the neutral, and thus we find that the 
apparatus on both sides has been supplied by the 30 amperes, 
and in such manner that fuse 1 carries 30, fuse 2 10, and fuse 3 
20 amperes. 

As soon, however, as we attach a 25 ampere arc to F, the 
10 amperes overbalance from the other side ceases to flow 
back over the neutral and begins to burn in series with the 
arc, which makes 30 amperes on the D, E, F side, plus the 
added 15 amperes required to make up the 25 ampere arc, or a 
total of 45 amperes, so that we have, under that condition, 30 
amperes on the A, B, C side outside wire, and 45 amperes on 
the D, E, F side outside wire and 15 amperes flowing out 
from the dynamo on the neutral. Therefore our 60 ampere 
fuse would, as a matter of fact, still be altogether too large 
to properly protect the apparatus. It would require a 40 
ampere arc to work fuse 3 to capacity. To be fused absolutely 
right under those conditions we should have a 30 ampere fuse 
on one outside wire, a 45 ampere fuse on the other and a 15 
ampere fuse on the neutral, but this, of course, is never done 
in actual practice, since the load carried by fuse 2 would vary 
with every lamp or motor shut off on either side, and the 
apparatus is supposed to be protected by its individual circuit 

Notes Now don't start trying to tear this to pieces on 
technicalities. It is under standdbleness I am after, rather than 
strictly technical correctness. 

If your theatre is fed by a three-wire system you should 
see to it that the two sides are as nearly as possible balanced. 
If they were perfectly balanced your neutral fuse could blow 
without affecting the lights in your house, but if the neutral 


fuse blows and the system is unbalanced then the effect is 
that of forcing the lights on one side above candle power 
while those on the other side will burn below candle power. 


To figure wire sizes for three-wire circuits you should pro- 
ceed the same as for ordinary two-wire systems (page 55), 
considering only the two outside wires and the amperage 
necessary to operate the apparatus at 220 volts; then, having 
determined the size of the two outside wires, make the center 
wire the same size. 

Go to your work each day 
as though it were your 
first day on a new job 
and you had to make good. 



THERE are a few points of importance concerning 
switches to which the operator's attention should be 
forcefully directed. I emphasize the "forcefully" be- 
cause I have seen these things neglected, with consequent 
heating and even burning at the switch contacts, in all too 
many operating rooms. 

In Fig. 13 we see, at the left, an ordinary single-pole, single- 
throw knife switch, in which A is the. blade of the switch, B 
the handle, C the contact, D the hinge, E-E the terminals to 
which the wires are attached, and F the insulating base, 
which may be slate, porcelain, marble or any other high 
grade insulating material suitable for the purpose. At the 
right is a single-pole switch with a second contact, so that 

Figure 13. 

blade A may be thrown over to make a contact on the other 
side. Instead of being a single-pole, single-throw switch it thus 
becomes a single-pole double-throw switch, or, as ordinarily ex- 
pressed, a S. P. D. T. switch. 

If a switch has two blades, connected by a cross bar of 
insulating material to which the handle is attached, as per A, 
Fig. 14, then it is a "double-pole" instead of a single-pole 
switch. If it has three blades, as per B, Fig. 14, it would be 
a "triple-pole" or "three-pole" switch, and so on. C, Fig. 14, 
shows a double-pole single-throw (D. P. S. T.) switch 
equipped with contacts for knife-blade cartridge fuses, such 
as are shown at B, Fig. 22; D shows a double-pole 
single-throw switch with ferrule contacts for cartridge fuses. 
Switches with contacts for link fuses may be had instead of 
for cartridge or plug, and may be used for projection cir- 
cuits, if such circuits are to be protected by link fuses, thus 



obviating the necessity for a separate fuse block; E and F 
show types of porcelain base single-throw, double-pole 
switches with plug fuse receptacles. These switches are 
called "panel cut-outs," and may be used to control individual 
circuits of low amperage. 

Figure 14. 

Inclosed Switches. An inclosed switch is one with an in- 
dividual covering, usually of sheet metal, which entirely in- 
closes the switch-blades, contacts, etc. This is the type used 
for the projection machine table switch. The covering is to 
protect the operator from accidental contact with live parts 
of the switch, and to prevent accidental short circuits. With 
inclosed switches it is important the covering be so made 
that it cannot come into contact with the live parts of the 
switch, since if both blades or two contacts of opposite polar- 
ity come into contact with the metal, a direct short circuit is 

In connecting inclosed switches it is very much better that the 
blade end of the switch be dead when the switch is open. In 
fact, that rule applies to all switches, though sometimes circum- 
stances prevent its being adhered to. 

Proper Location of Switches. This is a difficult matter to 
deal with intelligently, since local conditions must very 


largely govern. In general, however, it may be said that the 
house switchboard should be so located that the man in 
charge will have an unobstructed view of the screen when at 
the switchboard. This is of particular importance, since 
otherwise it will be found very difficult properly to handle 
the lights at the beginning .and end of the show, or at the 
beginning or end of individual reels. 

Switches governing emergency lights (exit lights and all lights 
kept burning during the performance) should under no circum- 
stances be placed on the main switchboard. You can never tell 
what an excited man will do, and in case of fire, people inside the 
auditorium, including employes, are usually excited. 

Place the emergency light switches in the box office where no- 
body can get at them but the ticket seller, and make him or her 
directly responsible for their proper handling. 

In the operating room local conditions will govern the plac- 
ing of the switches, but it may be said in general there is 
nothing to be gained by making things inconvenient for the 
operator, and wrongly located switches often cause much 
entirely unnecessary labor .and annoyance. 

The operating room incandescent lights should be governed by 
one switch, -located where it can easily be reached from operating 
position at either machine. There should also be individual snap 
switches on each lamp socket. 

This is of much importance, because it is utterly impractical, 
not to say impossible, to have high class projection with incan- 
descent lights burning in the operating room, and the operator is 
much more likely to extinguish his lights if there is a switch 
handily located with which he can put them all out at one opera- 
tion than he is to put out two or three lights by means of their 
individual socket switches. This is one of the seemingly simple 
points which is of great importance in its bearing on results on 
the screen. 

NEVER install a knife switch in such way that its handle 
moves upzvard in opening the switch. 

If it be a single-throw switch, install it so the handle hangs 
down when the switch is open. If it be a double-throw switch 
install it so the handle swings sideways. This obviates the 
danger of the switch accidentally falling shut. 

Uses of Types of Switches. The use of the single-pole 
switch except for certain purposes is prohibited by Under- 
writers' rules, and none of those purposes exist in theatres, 
I think, except that the single-pole switch is of use in the 


making of certain rheostat connections, as will be explained 
under another heading. 

The double-pole single-throw switch is the type ordinarily 
used to control incandescent and projection circuits, and, in 
fact, for practically all theatre circuits, except those con- 
trolled by a triple-pole, or by a double-pole, double-throw 
switch. The triple-pole single-throw switch is used to con- 
trol three-wire circuits where they enter the theatre, and 
wherever else the three-wire circuit may extend. The double- 
pole double-throw switch is used in certain fuse connections, 
as will be explained under "Fuses." It is also of use for con- 
necting two separate two-wire supply systems, and for pro- 
jection circuit connections under certain conditions. 

Underwriters' Rules require that switches have certain di- 
mensions, according to the voltage and amperage they are to 
handle. Both the voltage and amperage capacity must be 
stamped on some part of knife switches. 

Figure 15. 

Fig. 15 illustrates how switches are marked. Reject any 
switch not so stamped. A switch may be used for a less am- 
perage and less voltage than its stamping, but never for higher 
voltage or amperage. The higher the voltage the farther 
apart must be the knives of the switch, and the longer they 
must be. Two hundred and fifty-volt switches are the kind 
almost universally used in theatres. There is no such thing 
as a 110- volt switch, the requirements for 110 and 220 being 
the same. 

At the right in Fig. -15 we see an illustration of a switch 
equipped with fuse link contacts. This is the kind of switch 
that is used on projection circuits where the circuit is con- 
trolled with link fuses. 

Care of Switches. Referring to Fig. 13, hinge D must be 
kept tig^ht tight enough so that it requires a slight effort 
to move the handle. Contacts C must be kept in good con- 
dition and must grasp blade A firmly when the switch is 
closed. If these contacts become loose there will be heating, 


loss of power and roughening of both the contacts and the 
blades, as well as an increase in the resistance of the copper 
by reason of continuous heating. It is very important that 
hinge D be kept tight, because otherwise when you close the 
switch the blade is likely not to strike contacts C squarely 
and enter quickly, with consequent arcing and burning of the 
copper. Use a little common sense and good judgment in deal- 
ing with your switches. Should these contacts become rough by 
arcing, they may be carefully smoothed with a very fine, thin 
file, or a piece of or 00 emery cloth wrapped around a thin 
piece of metal. It is important that the cross bar of the 
switch be kept tight. A loose, wobbly switch is an abom- 
ination, and conclusive evidence of a careless, sloppy work- 

Metal Cabinet. All operating room switches and others, 
except the stage switchboard, should be inclosed in a metal 
cabinet, Fig. 19, Page 72, equipped with a door which auto- 
matically closes either by power of the springs or action of 
gravity. It is a good plan to examine the switches, say, once 
a week, tightening all loose joints and cleaning off all dust. 
This may best be done either with a bellows or brush. 


IT is essential that both the theatre manager and operator 
have a very good understanding of the main switchboard. 
In many of the larger houses the main switchboard is a 
large, imposing arrangement, which looks very formidable. 
As a matter of fact, however, these boards are quite simple 
and easily understood, if one examine them closely, keeping 
in mind his knowledge of electrical action. On Page 10 of 
the "National Electric Code," a copy of which may be se- 
cured free by sending stamped, self-addressed envelope to 
the National Board of Underwriters' office, William Street, 
New York City, appear the following rules, which must be 
strictly observed in the installation of switchboards: 

a. Must be so placed as to reduce to a minimum the danger of communi- 
cating fire to adjacent combustible material. 

Switchboards must not be built up to the ceiling, a space of three feet being 
left, if possible, between the ceiling and the board. The space back of the 
board must be kept clear of rubbish and not used for storage purposes. 

b. Must be made of non-combustible material. 

c. Must be accessible from all sides when the connections are on the back, 
but may be placed against a brick or stone wan when the wiring is entirely 
on the face. 


If the wiring is on the back, there must be a clear space of at least 
eighteen inches between the wall and the apparatus on the board, and even 
if the wiring is entirely on the face, it is much better to have the board 
set out from the wall. 

d. Must be kept free from moisture. 

e. Wires with inflammable outer braiding, when brought close together, 
as in the rear of switchboards, must, when required, be each surrounded 
with a tight, non-combustible outer cover. 

Flame proofing must be stripped back on all cables a sufficient amount to 
give the necessary insulation distances for the voltage of the circuit on 
which the cable is used. 

The proper location of the main house switchboard will 
depend entirely upon local conditions, and may only be prop- 
erly determined by considering each individual case. The 
location which will be suitable in one theatre might not be 
so in another. In fixing the location the manager should be 
guided largely by the items "accessibility'* and "convenience," but 
it is essential that the board be so located that the man handling 
it will have a good view of the screen or of the stage when at his 
post of duty. This latter is very essential to the best manipula- 
tion of the lights, particularly if there be vaudeville. 

In some theatres the house switchboard is located in the 
operating room, but this I do not consider as being the best 
practice. The house switchboard should be located below, 
but a portion of the .auditorium lights should be so arranged 
that they may be handled from both the main switchboard 
and from the operating room. An emergency may at any 
time arise in which it is imperative that the auditorium be 
lighted instantly, as for instance, in case of fire. This can, of 
course, be done by the switchboard tender below, but there 
would probably be more or less delay in the response, and, 
moreover, the signal bell might "go wrong" just at that time. 
I do not, however, favor the placing of the main board in the 
operating room under any conditions. 

Except there be good reasons for not doing so, every cir- 
cuit in the theatre, including the operating room and stage 
feeders, but excepting the emergency lights (emergency 
lights are the exit lights and those ordinarily left burning 
during the performance, such as foyer, hall-way .and side 
lights), should pass through the main house switchboard. 

On the main house switchboard should be (a) the main 
fuses, located ahead (on the street side) of everything, ex- 
cept the exit and emergency lights, and carrying the entire 
house load; (b) the main switch, which kills everything but 
the exit and emergency lights; (c) fuses for every individual 
circuit in the house, including the operating room and stage 



feeders; (d) service switches for every individual circuit, ex- 
cept the operating room and stage feeders; (e) a switch gov- 
erning all auditorium circuits ordinarily extinguished during 
the performance, except where the auditorium lights are 
handled from the stage. This latter clause, however, may 
be considerably modified by the peculiarities of requirement 
in individual installation. In small, strictly moving picture 
houses, it is much better to have the auditorium lights extin- 
guished .all at one time, rather than by pulling half a dozen 
small switches. In large houses, however, where there are 
many incandescent lights and circuits, this is not a practical 
thing to do, and a dimmer should be used. 

Figure 16. 

In Fig. 16 is seen both a diagrammatic and photographic 
representation of ,a small three-wire switchboard, or "panel" 
board. In the diagram, A is the fuse contact, B the main 
switch, C-C the house circuit fuse contacts, and D-D the ser- 
vice switches on the individual incandescent circuits, all of 
which are seen photographically represented at the right, 
excepting that the main switch and fuses are omitted. Both 
in the diagram and photograph you will take note of the screw 
heads connecting feeder bars to the circuit bars. This is the 
secret of the whole thing. The left hand bar of the diagram 
crosses three bars and attaches to the fourth; the center bar 
crosses one bar and attaches to the two center bars, and the 
right hand bar attaches to the lower cross bar. Now the ap- 
plication of a little horse sense to this will show you that 
the two top cross bars take current from the left hand out- 
side feeder, or "bus bar," and the neutral, which forms a two- 
wire circuit leading both ways from the connection. The 




two lower cross bars .attach to the right hand outside feeder, 
or "bus bar," and the neutral, which forms another circuit, on 
"the other side" of the system, leading both ways from the 

In examining any switchboard, just look at the contacts, or 
the screw heads, for they will show you how the whole thing 
is connected. It is very easy, after you have a little practice, 
but it is a mighty puzzling thing to the beginner. 

Fig. 17 is the representation of a large, somewhat com- 
plicated board. On one side the individual circuits are in- 
dicated. Study the contacts and you will be able to trace out 
the connections. Taking the top right hand switch, 'for 
example, we find the circuit starts off as a three-wire circuit, 
through fuses and a triple-pole switch, which latter controls 
the circuits. It then splits into two two-wire circuits, each 
having their own fuses, because fuses must always be estab- 
lished on individual circuits, or where wire sizes change. The 
lower wire of the upper two-wire circuit and the upper wire 
of the lower two-wire circuit attach to the neutral, and the 
upper wire of the upper and the lower wire of the lower two- 
wire circuit to the outside wires of the three-wire circuit. 
Remembering that the neutral is positive to one outside wire, 
and negative to the other, we instantly see that the two upper 
and two lower wires are mates, that is to say, they are pairs, 
forming two two-wire (multiple arc) circuits. We also see 
that we cannot extinguish the lights on one circuit without 
extinguishing the lights on the other, except that we remove 
the fuses on one of the circuits, this latter by reason of ab- 
sence of individual circuit service switches. 

Just below the center of the board is a bank of circuits 
tapped off as two-wire circuits right at the bus bars. By 
observing the location of the screw heads we see which side 
each circuit connects to. We see there are four screw heads 
in each outside bus bar in this bank of two-wire circuits, 
therefore there are four circuits on either side, and these cir- 
cuits, provided each carries appliances using the same total 
amperage, is said to be "balanced." At the bottom we see a 
three-wire lead with fuses, but without switch. This is prob- 
ably the stage or operating room lead, which should not have 
a switch on the main house board. The main switch and 
fuses controlling and protecting the entire board are not 

In the smaller theatres it is common practice to build up a 
switchboard out of porcelain-base panel cutouts, such as is 



illustrated in Fig. 18. Any number of blocks may be used. 
They must be placed in a substantial metal cabinet, similar 
to the one shown in Fig. 19. Back of the blocks should be a 

Figure 18. 

layer of sheet asbestos, or .asbestos millboard, not less than 
three-eighths of an inch thick. If properly put together such 
a board is just as efficient, though it does not look as well, 
as the regular board built on a slate base. Ahead of a board 
of this kind should be the main switch, and a cutout block 
carrying the main fuses. 

Exit and Emergency Light Boards. The feeders for these 
circuits must be tapped to the main feeders on the street side 
off the main house fuses. 

They must be controlled by switches located in the box office, 
and by no other switches. 

For further information concerning this subject see Fig. 28, 
Pages 85 and 86. 

Figure 19. 

Illustrating small panel boxes and switchboards. 



Stage Switchboard. The stage switchboard should be 
located on the proscenium wall. It is common practice to 
place it to the right of the stage as one looks toward the 
audience. It should be protected by a substantially con- 
structed iron railing, not less than 48 inches high and located 
not less than 36 inches from the face of the board, and to be 
securely fastened to the floor in such manner as to withstand 
a heavy shock, as, for instance, a person falling violently 
against it, or scenery falling on it. 

All fuses on a stage switchboard must be approved cartridge or 
plug type. It is absolutely forbidden, under any circumstances, 
to use a link or open fuse on the stage. 

The stage switchboard should carry (a) main fuses and 
main switch supplying all stage circuits; (b) service fuses 
and switches for each individual circuit, plainly labeled with 
name of circuit it controls, thus: "White Foots," "Red 
Foots," "First Borders, White," "First Borders, Green," etc. 

Stage switchboards need not be equipped with a cabinet and 
door, but every precaution must be observed to render acci- 
dental contact with scenery impossible. The utmost care 
must be exercised that all switch contacts and wire contacts 
and fuse contacts be kept tight .and in perfect electrical and 
mechanical condition, to prevent any possibility of heating. 
The wires should be thoroughly examined at regular inter- 
vals to see that the installation is in perfect condition. In 
fact, inasmuch as there is always more or less (usually more, 
and sometimes a great deal more) inflammable material con- 
stantly exposed on the stage, it is impossible to be too care- 

jigure 20. 


ful with the electrical installation and in assuring its main- 
tenance in perfect condition. 

Absolutely no one except the man in charge of the stage 
switchboard should be allowed to touch it while a perform- 
ance is under way, and the fewer persons handling it at other 
times the better. Stage switchboards should always be wired 
from the back. This is not absolutely necessary, but it looks 
better and if better. This also is true of the main house switch- 
board. It is not necessary that an expensive marble board 
be purchased. 

Fixtures such as those illustrated in Fig. 20 may be had 
from any dealer in electrical supplies. You may then pur- 
chase a marble or slate slab of your local dealer, first having 
ascertained the length of the fixture bolts so that a slab of 
proper thickness may be selected. Having secured such a 
slab, any man of ordinary intelligence can lay out and drill 
the holes. Affixing the fixtures to the slab is then merely a 
matter of placing the bolts in the holes and tightening the 

For a small board, one-half inch asbestos millboard makes 
a fairly good support. If it is a main) house switch- 
board the sides of such a board must afterward be covered 
with a metal rim to receive a metal door. If rightly done 
such a board will not be excessive in cost and will look very 
much better than a board built up of blocks as per Fig. 18. 
First lay out the board on paper, just as you want it, loca- 
ting all the holes carefully, then lay the paper on the marble, 
slate, or whatever base you use, mark the holes, and drill 
them. Manufacturers will, upon request, supply you with a 
catalog giving the dimensions of fixtures such as are shown 
in Fig. 20. 

A general idea of the layout of a small moving picture 
theatre switchboard is had from Fig. 21, in which X-X-X-X, 
etc., are circuit switches, carrying fuses, and Y and Z fuses 
and switches on the stage and operating room circuits. 

A small gas plier is the handiest tool with which to remove 
and insert cartridge fuses. Wrap the handles of the pliers with 
insulating tape to avoid possibility of shock. 

If a fuse blows and you are not certain which one it is 
touch your test lamp terminals to the fuse terminals before mov- 
ing either fuse and without opening the switch. If the lamp 
lights that's the fuse. If it doesn't then it is the other fuse. 
If it lights on neither then either both fuses are blown or 
the circuit is open somewhere. To make this test on pro- 
jection circuit fuses the carbon must be frozen. 



\ ( 


Figure 21. 




AS has already been set forth, an electric conductor will 
only carry a certain given number of amperes of cur- 
rent without developing heat. See Table 1, Page 42. 
Ordinarily only the quantity of current consumed by the 
motors and lamps attached to the circuit will flow over the 
wires of the circuit, and the capacity of the lamps and motors 
is never presumed to exceed the rated capacity of the wires. 
However, many things, such ,as grounds, short circuits, or a 
rise in the voltage may occur to cause a rush of current suf- 
ficient to overload the wires, or, in the case of rise in voltage, 
overload the apparatus attached thereto, and possibly the 
wires as well. The fuse is .a sort of automatic safety valve 
designed to take care of just this sort of thing. 

Figure 22. 

In Fig. 22 we see the principle of the fuse illustrated. The 
wires of the circuit are cut and their ends attached to ter- 
minals A-A-A-A fastened to slate base B. Under these 
terminals are clamped two pieces of fuse wire composed of 
an alloy of metals having very low melting temperature and 
a high temperature coefficient, which means that their re- 
sistance rises very rapidly with increased temperature. The 
operation is as follows: The current capacity of the fuse 
wires is in no case presumed to exceed the rated capacity 
of the wires of the circuit they protect (See Table 1) and to 
only exceed the combined current consuming capacity of the 
lamps attached to the circuit by a small margin, and to only 
exceed the combined current consuming capacity of the 
motors by 25 per cent. 

Assuming, for example, a circuit the wires of which are 
rated at 6 amperes R.-C., and that a sufficient number of in- 
candescent lamps are attached to consume a total of 5 amperes, 
we would insert a 5-ampere capacity fuse wire between the 
terminals of our block, Fig. 22. Such fuses would actually 
carry a little more than 5 amperes, because fuses are designed 

TABLE No. 4 






3 5 



Z "oj 


I uuoj 

2 raj 



. w 


c3 O, 



I "OJ 




to carry a 10 per cent, overload in excess of their rated ca- 
pacity, in order to allow for ordinary fluctuations in voltage. 
Now suppose a short circuit or ground occurred somewhere 
on the circuit, which would cause a rush of current and over- 
load the wires, or suppose there is a heavy rise in the voltage, 
which would have the effect of forcing more current through 
the resistance of the lamps, thus overloading the wires, 
with possibility of results more or less disastrous. What 
happens? Why, just this: The fuse wire is overloaded 
and becomes hot, whereas no damage would be done to 
the copper wire until it reached a temperature, far in 
excess of that which would melt the fuse wire, therefore 
both the wires of the circuit and the lamps are pro- 
tected by reason of the fact that the fuse wire melts and 
automatically stops all flow of current, thus "cutting out the 
circuit." Nor can a new fuse be installed until the trouble 
has been remedied, since if an attempt be made to install a 
new fuse without removing the seat of the difficulty it would 
promptly melt (blow) and again stop the flow of current. 
That is the theory of the fuse, as well as its practical opera- 
tion, though raw fuse wire is not employed in theatres, except 
in the "link" fuses used in some cities to protect projection 
lamp circuits, the same being located in an iron cabinet in 
the operating room. 

Safety fuses are made in a number of forms, but those with 
which the moving picture operator comes into contact are 
known as the "plug" or the "cartridge," both these forms 
being in general use in theatres. 

Figure 23. 

In Fig. 23, A, B, are cartridge fuses with different styles of 
terminals, A, the "ferrule" contact, only being allowed on 



circuits carrying 60 amperes or less. C and D are receptacles 
for A and B. B is the "knife-blade" contact fuse. 

Cartridge Fuses. A cartridge fuse consists of two metal 
terminals joined by a paper barrel. Inside this barrel is the 
fuse wire, connecting the two terminals, with a small pilot 
wire passing under the round spot on the paper label, as is il- 
lustrated in Fig. 24. An air chamber is used in some fuses, 
the idea being that the heat conduction through the confined 

Figure 24. 

air being slow, the temperature in that part of the fuse will 
rise rapidly and always in the same ratio, thus establishing 
a practically constant point of blowing. 

The fuse wire is surrounded by a powdered, non-conducting 
substance designed to instantly break the arc when the fuse 
blows. On the paper label on the outside of the barrel is a 
small round spot, under which the pilot wire passes. When 
the fuse blows the pilot wire is supposed to melt and turn the 
spot black, but it doesn't always do it. 

Table 4 gives an idea of the essential points in a cartridge 
fuse. The Underwriters require that the contacts have a cer- 
tain area, that the paper barrels have a certain length and 
diameter, and that the fuses have a certain length over all 
for a given voltage and amperage. Table 4 is taken bodily 
from the "National Electric Code." 



The plug fuse, A, Fig. 25, consists of a porcelain base with a 
brass screw, and a center contact at its lower end, with a 
protecting brass cap at its upper end, the latter usually hav- 
ing a clear mica center so that you can look through and see 
if the fuse wire is intact. Ordinarily, however, you cannot 
do anything of the kind with .any degree of certainty, any 
more than you can depend with certainty on the spot of the 
cartridge fuse turning black when the fuse blows. The only way 

Figure 25. 

is to test a fuse in the manner set forth further on. B, Fig. 25, 
shows the receptacle for plug fuse A, and C a fuse with the 
cap off, showing fuse wire. D is a special form of plug fuse 
to be used with amperage between 35 and 60. Plug fuses, in 
their regular form, A, Fig. 25, are not made in excess of 35 
amperes capacity. They are not made in any form for capac- 
ity in excess of 60 amperes. Plug fuses may be used for any 
kind of work up to the limit of their capacity. They are per- 
fectly safe, and somewhat cheaper than the cartridge fuse. 


The link fuse, Fig. 26, provided its receptacle be placed in- 
side .a metal box having a metal cover, is perhaps the best 
fuse to use for the projection circuit; this for several reasons, 
not the least important of which is the fact that it cannot 


readily be "boosted" without the trick being plainly visible 
to the inspector. In other words, the link fuse is very largely 
fool-proof. With both the plug and cartridge fuses it is quite 
possible for operators possessed of more cunning than good 
sense to increase the capacity of their fuses almost indefinitely 
by placing a short piece of copper wire, or sheet copper, called 
a "jumper" in the terminals in such manner that it is under 
the fuse, hence out of sight. Such a trick could only be de- 
tected by close inspection, which is not "true of the link fuse. 
The plug fuse may be boosted after the same fashion by 
placing a copper penny inside the receptacle and screwing 
the plug down on it in such manner that the two contacts 
are connected by the copper. Such tricks as this, however, 
render the fuse of no value, and leave the circuit to all intents and 
purposes entirely unprotected. They cannot be too strongly con- 
demned, and any operator or other person caught boosting fuses 
ought to be instantly discharged and have his license, if he have 
one, revoked. By reason of the difficulty in boosting a link fuse 
the Department of Water Supply, Gas and Electricity of the City 
of New York has issued a rule compelling the use of link fuses 
on projection circuits where the current used exceeds the capacity 
of the ordinary plug fuse, viz., 35 amperes. Both fuse blocks and 
switches may be had to carry link fuses. (See Fig. 15.) 

Never fuse above the rated capacity of the wires of the circuit. 
Never fuse an incandescent lamp circuit above the combined am- 
perage capacity of its lamps. Never fuse a motor circuit above 
the rated capacity of the wires, or more than 25 per cent, above 
the rated capacity of the motor or motors. 

Underwriters' rules allow the fusing of the motor circuit to 
25 per cent, above the capacity of the motor, or the combined 
capacities of two or more motors, provided, of course, the 
wires are large enough. 

It is physically possible to refill both the cartridge and plug 
fuse, but it does not pay to do so. The only safe rule is : 

Throw all blown fuses away. There will then be no mixing 
zvith the good ones, with consequent vexatious delays. If you 
mix your good fuses with bad ones you are more than apt to 
have such delays, which may and probably will happen just at 
the very worst possible time, and be chargeable entirely to your 
own carelessness. 


The projection circuit offers nothing in any way susceptible 
to damage through momentary overload. It is a nuisance to 



have fuses constantly blowing, and, since the resistance of 
the hand-fed arc lamp is a variable quantity, current flow will 
under any condition vary considerably. I would therefore 
recommend for projection circuits the following, with the 
understanding that the current flow at the arc is what is re- 
ferred to under the heading "Normal Amperage." Of course, 
if the fusing is only done on the primary of a transformer 
(economizer, compensarc, inductor, etc.) then due allowance 
must be made. 


Operating room fuse capacity where rheostats are used for 

Necessary size as- 

. beskos covered 

Normal Arc portion of cir- portion of cir- 

Amperage Fuse to cuit wires cuit wires 

20 25 6 6 



Necessary size R.C. 

Fuse to 

portion of cir- 
cuit wires 



















Explanation of Table 5 : Wires must be large enough to ac- 
commodate the fuse capacity without overload. That portion of 
the circuit which is asbestos-covered wire may be treated as 
weather-proof in this respect. 


This is a simple matter. Ordinarily there are fuses both 
on the intake and output lines on the motor and generator 
side. Ascertain the amperage at your arc under normal con- 
ditions, and add about 20 per cent, of that amount, which will 
give the size for your fuses on the generator or output side. 
The arc will, of course, be D. C., hence 48 volts. Therefore 
the arc amperage multiplied by 48 will give the arc wattage, 
which, divided by the intake (line) voltage, will give the in- 
take amperage, or would give it if the machine had 100 per 
cent, efficiency. Few machines, however, have more than 65 
per cent, efficiency; therefore to this must be added 35 per 
cent, in order to get the actual intake in amperage, thus: 
Assuming a line voltage of 110 and an arc wattage of 1920, 
then 1920 watts -^- 110 volts = \7 l / 2 amperes, and 35 per cent, 
of \7 l / 2 amperes is 6 l / 2 amperes and \7 l /2 + 6 l /2 = 24, therefore 
the intake amperage, based on the assumption that the 


machine has 65 per cent, efficiency, is 24, but we will install 
30 ampere fuses, since the Underwriters approve of fusing 
a motor 25 per cent, above its actual capacity. 

The following must be qualified, however, by the fact that 
if the generator is of higher voltage than the arc, then the 
arc amperage must be multiplied by the voltage of the 
generator instead of the voltage of the arc, since resistance 
will have to be used to cut down the voltage to 48, and vol- 
tage wasted in resistance counts just the same as that used 
in operating the arc. 

Plenty of fuses should be kept on hand. You never can tell 
when one -will blow, and sometimes a sort of epidemic of fuse 
blowing occurs. It is very awkward to get caught without fuses, 
and the only insurance against it is a good surplus stock, but be 
very careful that blown fuses don't get mixed with the good ones. 

In case you do get caught without fuses you can protect the 
circuit temporarily with one fuse, bridging the two other fuse 
terminals with copper wire. This is by no means a good con- 
dition, and may only be tolerated temporarily, in case of emer- 
gency, until the proper fuses can be procured. Such a condition 
would, in fact, be very bad, and emergencies of this kind never 
ought to occur. It is possible to make a fuse of copper wire, 
and while such a fuse would be to a considerable extent unre- 
liable, and from every point of view objectionable, still it may be 
used temporarily in an emergency, therefore I give the fusing 
point of small copper wires. 


Fusing Point of Copper Wires. 

American (B. & S.) Wire Gauge Fusing Current in Amperes 

30 10 

28 15 

26 20 

25 25 

24 30 

22 40 

21 50 

20 60 

19 70 

18 80 

17 100 

16 120 

1" 140 

14 160 

13 200 



By adding two copper wires of different sizes together, 
fuses of almost any desired strength may be had, thus: A 
No. 30 and 17 wire combined would make a 47 ampere fuse. 


Should a fuse blow and upon installing a new one it also 
immediately blows, it is conclusive proof there is heavy over- 
load, most likely due to a heavy short or ground, and the 
circuit must be left dead until the trouble is remedied. You 
will most likely find the difficulty exists in the form of a 
ground, or a short caused by something of current carrying 
capacity connecting the wires at some exposed point. A 
ground, will, however, be the most likely cause of the trouble. 
(See Testing for Grounds.) 

A rise in voltage will operate to force more current 
through the lamps and motors, thus causing an increase in the 
amperage, which may blow the fuses. It will be evidenced 
by the incandescent lamps burning above c.p. Should a fuse 
blow and the new one installed also blow after a few min- 
utes, or an extended time, first of all examine the fuse contacts, 
as loose or dirty contacts will generate heat which may be suf- 
ficient to cause the trouble. 

Fuses will sometimes blow and it will be difficult to tell 
which one of the two it is. I would recommend the installa- 
tion at some convenient point to the main switchboard of a 
fuse tester made as per Fig. 27. 

Figure 27. 


A and B, Fig. 27, are wires of any circuit that is always 
"alive," preferably the main theatre feeders ahead of the 
switchboard fuses. If you attach at that point and the house 
is fed by a three-wire system, be sure to attach to one out- 
side wire and the central or neutral wire, else you will have 
220 volts on your tester; D is an ordinary cartridge recep- 
tacle; E a plug fuse receptacle; C an incandescent lamp of 
the voltage of your current. When you put a fuse in either 
of the receptacles and lamp C does not light the fuse is 
worthless and should be thrown away. 

Cartridge fuse voltage and amperage rating are usually found 
on a paper label on their barrel; the plug fuses .have their 
rating stamped on the brass cap, and link fuses have or 
should have their rating stamped on one of the copper con- 
tacts at their ends. 

Fuses are Ordinarily Installed as Follows: (a) Main ser- 
vice fuses, located ahead (on the street side) of the main 
switch. These fuses carry the entire load of the theatre, ex- 
cept the exit and other lights ordinarily left burning during 
the performance. Circuits carrying these latter, called emer- 
gency lights, should be attached to the feed wires ahead (on 
the street side) of everything else, and have service fuses of 
their own (see Page 86). In some houses the stage is fed 
by a separate set of feeders coming from the street mains, in 
which case these circuits will, of course, have main fuses of 
their own. (b) Fuses, usually on the main house switchboard, 
carrying the operating room feeder circuit, (c) Fuses, on 
the main switchboard, carrying feed wires for the stage, if 
the stage takes its current through the main switchboard, as 
is usually the case, (d) Main fuses in the operating room, 
which carry all operating room circuits. Also individual ser- 
vice fuses in each separate projection machine line and oper- 
ating room motor and incandescent circuit, (e) Fuses, or- 
dinarily located on the main house switchboard, on each in- 
dividual incandescent circuit, (f) Fuses on the stage switch- 
board for each individual circuit, as well as main fuses carry- 
ing all circuits except exit and emergency light circuits, 
(g) Fuses, usually located in the box office, carrying the en- 
tire emergency light system, as well as fuses for each in- 
dividual emergency light circuit, (h) Fuses for each individual 
emergency light, particularly in the case of exit lights, 
(i) Fuses must be installed wherever a change in size (diameter) 
of wire occurs. 



Main fuses for emergency light circuits should not be lo- 
cated on the house switchboard, but should be in the box 
office. In addition to this, every separate circuit must have 
fuses of its own, and, still in addition to this, it is an excel- 
lent scheme to fuse each individual emergency light, es- 
pecially the exit sign lamps, with 1 ampere fuses of its own, 
then if trouble should develop in a lamp, it will simply blow 
its own fuse without disturbing the other emergency lights, where- 
as otherwise it would, or at least might put out of commission the 
whole circuit, or possibly even the entire emergency light system. 

Every circuit, no matter how large or how small it may be, 
must be protected by its own individual fuses, in addition to the 
main fuses carrying all circuits. 

Plug or cartridge fuses are the only types it is permissible 
to use in a theatre, except that, unless local law prevents, 
link fuses inclosed in metal cabinet may be used in operating 
rooms for projection circuits. 

Figure 28. 

The blowing of projection circuit fuses is a very annoying 
thing, since it stops the show and causes delay while new 
ones are installed. It does not necessarily follow there is 
anything wrong because a projection circuit fuse blows, 
particularly if the circuit is not fused much above the am- 
perage being used. By installing two sets of projection cir- 
cuit fuses, as per Fig. 28, delays of this kind are avoided, be- 
cause one only has to throw over the switch to cut a new 
set of fuses, and unless there be something wrong with the 
circuit there is no appreciable delay. 




Both the lamphouse and rheostat terminals are subjected to 
considerable heat, therefore it is not practical to solder the 
lugs to the wire. There are a number of fairly good termi- 
nals made for use under such conditions, but those made to 
connect with the wire by bending over and squeezing down 
a set of copper lips, D-D-D, Fig. 29, are, as a general propo- 
sition, too light for use with the modern high amperage. 
The best non-solder terminals are those made of brass, or 
some composition metal, which have ample cross-section, and 
which clamp the wire either by tightening down on screws 
or by screwing up a section of the terminal. Among the best 
of these are those illustrated at A-A-A, B-C-C-C and E-E, 
Fig. 29, A-A-A and E-E being identical, except for the hook 
connection on the former. 

Figure 29. 

There are many other good lugs, these illustrated being 
merely examples. 

It is particularly necessary that the binding posts and ter- 
minals of the rheostat and arc lamp be kept perfectly clean, 
and, by reason of the fact that metal is likely to oxidize 
under the action of heat, both the rheostat and arc lamp 
connections should be taken apart about once a week and 
thoroughly cleaned, either by sandpapering or scraping. 
The operator should not neglect things of this kind. He 
may think they are of minor importance, but in that he is 
mistaken. It not only costs actual money through waste of 
power, but, also, by decreasing the arc amperage, injures the 
illumination of the screen. 


Wire Terminals 

EVERY wire ought to have a terminal lug, and ; except 
in cases where the same will be subjected to heat, as, 
for instance, in a lamphouse or on a rheostat, these 
lugs should be soldered to the wire. They come in a num- 
ber of forms, but almost any of them will serve the purpose 
very well if properly attached to the wire. In order to 
solder a lug to the wire proceed as follows: First measure 
the depth of socket in the lug, and cut off enough of the 
insulation of the wire to just let the end of the wire reach the 
bottom, scraping the bare end of the wire perfectly clean, 
until it shines. This latter is important, since otherwise the 
wire cannot make perfect electrical contact with the solder. 
Next, first having made sure the inside of the wire socket is 
perfectly clean, hold the lug in the flame of .a blow-torch or 
some other source of heat and melt sufficient solder into it 
to fill the hole .about half full. Don't get the terminal too 
hot, but just hot enough to make the solder thoroughly 
liiquid. Now, having put a little flux on the bare part of the 
wire, shove it down into the solder and hold it until it sets. 

Caution. Don't shove the wire into the lug with a quick 
push. If you do the solder will probably squirt out, and you 
may get badly burned. Warm the end of the wire and then 
shove it in firmly, but not too fast. If directions are fol- 
lowed you will have a perfect electrical joint. In attaching 
terminal lugs to binding posts always be sure that both the 
lug and binding post are perfectly clean. A little No. sand- 
paper or emery cloth will be found handy for cleaning con- 
tacts; also you can scrape them with a knife blade.. It is, 
however, exceedingly important that when a copper wire is 
joined directly to a -binding post it be perfectly clean, since 
ofttimes a thin coating of oxidation will cover the metal, 
and this coating, while it is almost thin enough to be in- 
visible, offers high resistance. The resistance of one such 
joint would not amount to very much, but that of a dozen 
would cost you a good many dollars in wasted energy in the 
course of the year remember that your meter registers all 
energy consumed, whether it be used in overcoming useless 
resistance or in the production of light and power. 



A wire splice is something every operator should know how 
to make correctly. An imperfect splice will heat and cause loss 
of power. It may cause the wire to burn off entirely. In any 
event it is a constant source of loss of energy through its ex- 
cessive resistance. 

A splice must be electrically perfect, and should in all cases, 
unless a strictly temporary joint, be soldered. 

In Fig. 30 several correct methods of making splices are 
illustrated. First, the insulation must be removed from the 
two ends to be joined, for a distance of from two to four 
inches, according to size of the wire. The insulation should 
be whittled away just as you whittle a lead pencil. Never 
cut the insulation square off by running the knife blade 
around the wire. This makes a very neat looking job, but 
the trouble is that the blade is likely to cut a slight ring 
around the wire, and this ring acts very much as a scratch 

Figure 30. 

on the surface of glass does, causing the wire to break very 
easily at that point. The correct method is shown at A, 
Fig. 30, and the incorrect at B. What is perhaps the best 
method of making a splice in asbestos covered, stranded wire 
is illustrated at C, Fig. 30, except that the strands should be 
divided into about six sections. 

After removing the insulation the wire ends must be thor- 
oughly cleaned, until they shine. This may be done with 
emery paper, or by scraping with a knife blade. But, however 
it is done, the wire must be made perfectly clean, else there 
will not be good electrical contact. The wire ends must 


then be twisted tightly together as at 1, Fig. 30, after which 
the joint must be soldered. Underwriters' rules provide that 
a wire splice must be made both mechanically and electrically 
perfect before soldering. After the joint is made, as per 
Fig. 30, proceed to solder it as follows: Wet it thoroughly 
with a soldering fluid, or its equivalent, which may be had 
from electrical dealers in stick form. An excellent soldering 
fluid is made of 

Saturated solution of zinc chloride 5 parts. 

Alcohol 4 parts. 

Glycerine 1 part. 

After thoroughly wetting the joint with the fluid, or rubbing 
on plenty of the flux in stick form, hold the wire in the blaze 
of a gasoline torch until warm, and then also hold in the 
blaze a piece ,of solder, which may be had of electrical deal- 
ers in wire form, until it melts and runs all through the joint. 
Care must be had not to get the wire too hot, ~ince, especially 
with the smaller wires, too much heat causes injury and 
reduces the carrying capacity; also if too hot the solder will 
run through and out of the joint. If the soldering is proper- 
ly done the joint will have more mechanical strength and as 
great carrying capacity as the wire itself. All joints must be 
soldered, except they be strictly temporary, say to use for one 
day only. After soldering, the splice must be wrapped with 
insulating tape, to the depth 'of the original insulation. One 
or two thicknesses of tape are not enough. If properly done, 
the use of a wire connector, D, Fig. 30, is permissible; but 
the soldered joint is best. Wire connectors must not be used 
for joining asbestos-covered, stranded wires, except the end 
of the wire be first run full of solder, thus binding the 
strands together in a solid mass. 

For wires connecting to switch, or other cold binding posts, 
lugs similar to E, F, G, Fig. 30, must be used, but before in- 
serting wire ends into connectors, or lugs, they must be thor- 
oughly cleaned by scraping with a knife blade, or polishing 
with emery paper. Where such lugs are used, the wire must 
be soldered into them. 

Keep always in mind the fact that unless a wire splice or 
joint be very carefully made it will heat more or less and 
cause resistance, which means constant loss as long as the 
splice or joint is used. The loss from one imperfect splice 
or joint may be slight, but the combined loss from several 
may amount to considerable. 



BROADLY speaking, the function of a lens is to receive 
upon every portion of its surface light rays emanating 
from every pinpoint of the surface of a more or less 
distant object, and to so reflect and direct these rays that 
the image of the object will be formed, either of equal, less, 
or greater dimensions than those of the original object, at 
a distance from the opposite side. 

There are many terms used in connection with lenses, but 
I think that, so far as the operator be concerned, only a few 
are of real importance. 

The Optical Axis of the lens is an imaginary line running 
exactly through the center of the diameter of the lens, or, in 
other words, the center of the lens, being precisely at 
right angles to its plane. Another way of expressing it 
would be that, understanding that the surface of a lens is 
always the surface of a segment of a true sphere, a line drawn 
from the exact center of the circles shown in Fig. 34 
through the exact center of either one of the two lenses 
shown would of necessity be the optical axis of the lens, 
because it would pass exactly through the center of the 
lens and be exactly at right angles to its plane. 

The Conjugate Foci refers to two points, one being the 
distance to the lens from a light source or object, and the 
other to the distance from the lens to the point where the 
rays from the light source, or object, are refocused into an 
image. Altering the distance of one of these points from 
the lens automatically alters the other. 

The conjugate foci are shown in Fig. 32, in which the 
object might be substituted for the image, without changing 
the general effect. The image would occupy the position now 
occupied by the object and vice versa. In a projection ma- 
chine the conjugate foci points of its objective lens are the 
film at the aperture and the screen. If an actual picture 
be placed on the screen and brightly illuminated and a piece 
of ground glass be placed over the machine aperture it would 
be found that an image of the picture would appear thereon, 
and if the picture be the size ordinarily projected by the 
lens at that distance, then the image will just fill the machine 


Refraction. A lens depends for its action on the fact that 
light rays traveling through a transparent medium of uni- 
form density will travel in straight lines until they enter, at 
an angle, a transparent medium of different density, where- 
upon, at the exact point of entry into the second medium, 
their direction will be changed and the amount of change 
will be in proportion to (a) the angle at which the ray enters 
the second medium and (b) the relative density of the second 
medium as compared with the first. If the angle at which the 
rays strike the second medium be slight the bending or 
refraction will be slight; if the angle be .heavy the bending 
(refraction) will be proportionately greater. If the differ- 
ence in density of the two mediums be slight the bending 
(refraction), due to this fact, will be slight; if the difference 
in density be great, then the bending of the rays will be pro- 
portionately greater. 

It is somewhat difficult to intelligently explain the reason 
for the bending of the light ray, nor do I know that from 
the operator's viewpoint it is necessary. Suffice it to say that 
light rays do bend under the conditions before named; there- 
fore, when light passes from air into glass at an angle or 
from glass into air at an angle, the ray is bent (refracted) 
and, as before said, the amount of bending will depend upon 
the amount of angle and the relative density or refractive 
index of the glass as compared to that of the surrounding 
air. The refractive index of glass is equal to the size of the 
angle made by the incident ray, divided by the size of the 
angle made by the refracted ray. 

In this connection it would be interesting to know whether 
there would be any actual difference as between the action 
of a lens used at sea level and one used at, say, the summit of 
Pike's Peak. Theoretically there would; practically, I doubt 
it. It is merely an interesting point, based on the fact that 
the amount of refraction depends partly upon the relative 
density of the two mediums. 

Back Focus. The "back focus" of a lens (commonly ex- 
pressed as B. F.) is the distance from the object (film in the 
case of the projector objective) to the first surface of the 
lens. This is a very important matter to the operator, since 
it is practically impossible for him to locate the point of 
equivalent focus (E. F.) in any given objective with accuracy; 
also it would be very difficult for the operator to measure 
the actual distance from the point of E. F. to the film with 
the lens in actual working position, and, since any given lens 
may work in a great many different positions (distance from 


the film), and these different positions of the objective re- 
quire special treatment in the matter of the condenser, it is 
highly important that the operator be able to make precise 
measurement of the lens position. This is made possible by 
using the back focus for the purpose, only using the E. F. 
to figure focal length of lens necessary to project a picture 
of given size at a given distance. 

Equivalent Focus. "Equivalent focus" is a term applied to 
lenses made up of two or more lenses, as the objective lens. 
It simply means that the combination will possess the same 
power of reduction or magnification possessed by a single, 
simple lens of equal focus. For example: if your objective 
is a 4J^ inch E. F., then it will, working under the same con- 
dition, project the same size picture that a single lens of 4J^ 
inch focus would project, the difference being that the single 
lens would not project nearly so good an image. Equivalent 
focus is of value to the operator for one thing, and one 
thing only, viz: in computing the focal length lens required 
to project a picture of given size at a given distance. 

In order to understand lens action it is necessary to get 
the "viewpoint," and that is a very difficult thing to impart to 
the student. Each infinitesimal pinpoint on the surface of 
a lens is, from an optical standpoint, an entirely separate 
proposition from every other infinitestimal portion of the 
surface of that lens, since, because of the fact that a lens 
has curvature, each pinpoint of surface offers a different 
angle to the light, and therefore gives a refraction slightly dif- 
ferent from that of the pinpoint next adjoining it, and a dif- 
ferent retraction from that of all other points on its surface as 

Remembering that the amount of refraction a light ray will 
receive upon passing from air to glass, or vice versa, will 
depend to a very large extent upon the angle at which the 
ray strikes the glass in entering, or strikes the air in leaving, 
and the further fact that, having entered the lens and re- 
ceived its refraction at the point of entry, the ray will travel 
(provided the glass be of even density, as it must be in a 
good lens) in a perfectly straight line until it. strikes the 
other surface of the glass and re-enters the air, where it is 
again refracted, it will readily be seen that the entire refrac- 
tion takes place at the point of entry and exit. It therefore 
follows that the refractive power of a lens depends entirely 
upon its surfaces, and that the glass underneath is of no 
value whatever, so far as refraction be concerned, except to 
act as a support for the surfaces. In fact in condensing 


lenses the glass is a distinct detriment, in that it absorbs 
light in proportion to its thickness, but this is a necessary 
evil, since in order to accomplish a certain degree of refrac- 
tion a lens must have a certain degree of curvature, and that 

curvature compels the 
use of a fixed amount 
of glass to act as its 

This statement, how- 
ever, must be qualified 
when it is applied to the 
Figure 31. objective lens, where 

combinations of crown 

and flint glass are used to correct faults. For instance : the front 
wide lens of an objective is very thick often as much as three- 
eighths of an inch of glass being used, although the surfaces 
could be carried in their relation to each other by a far less 
amount. I assume, however, that this thickness is due to the 
fact that it is necessary to have a certain amount of flint 
glass in proportion to the amount of crown glass used, in 
order to fully correct chromatic aberr.ation. 

Spherical Aberration. Spherical aberration is that quality 
of a lens which produces an uneven refraction or bending 
of the light rays at different portions of the lens. Rays 
passing through the outer edge of an uncorrected lens will 
be refracted or bent to 
such an extent that they 
will refocus at a point 
considerably nearer the 
opposite face of the lens 
than will those rays pass- 
ing through nearer the 
center or optical axis of 
the lens. (See Fig. 31.) Figure 32 

The effect of spherical 

aberration on moving picture projection is not as yet thoroughly 
determined. It forms an interesting topic for future study. 
Spherical aberration is overcome or corrected by combining a 
concave lens with one having convex surfaces. These lenses 
must be so proportioned that the excessive converging powers 
of the outer surface of the lens is just counterbalanced by the 
diverging effect of the concave lens. (See Page 98.) 

Chromatic Aberration. Chromatic aberration is that qual- 
ity of a lens which causes it to separate white light to a 


greater or less extent into its primary colors. Chromatic 
aberration may be corrected or eliminated by a combination 
of flint and crown glass. 

The objective lens is corrected for both spherical and 
chromatic aberration, and that is the reason for the four 
lenses and their different shapes. The form of the lenses 
corrects spherical aberration and their composition corrects 
chromatic aberration. 

Now, assuming the lens in Fig. 32 -to be free from spher- 
ical aberration, all the rays emanating from any point on 
light source X and striking the surface of the lens will be 
refracted in such manner that they will meet again at point 
Y, these two points being called the "conjugate foci" of the 

lens. If light source X 
be advanced nearer the 
surface of the lens, point 
Y, at which the rays meet 
again, will be automatic- 
ally moved further away 
from the lens, and if 
point X, the light source, 
be brought near enough 
to the lens, point X final- 
ly will be lost, and rays 
will emanate from the 
lens in parallel, or even 
in diverging lines. On 
the other hand, if light 
source X be moved 
back further from the 

lens, point Y will be brought closer to its surface. In this 
connection a point of much importance in projection is the 
fact that, while the foregoing is strictly true when the light 
source is a pinpoint, it is subject to complications and 
modification in practice, because with a light source, say 
three-eighths inch in diameter, the rays emanating from a 
given point on one side of the crater will strike a given point 
on the lens at a different angle than will rays emanating from 
a given point on the opposite diameter of the crater. Just 
what and how much practical effect this has on projection I 
do not know, but certainly it has some, and forms an inter- 
esting topic for study. For one thing the large light source 
serves to secure a reasonably even illumination of the film 
picture, which would, due to spherical aberration in the con- 
denser, be impossible with a very small crater. 

Figure 33. 



At A, Fig. 33, we see a "long focal" length lens, which 
means one having slight curvature. Its refractive powers are 
not so great as the lens shown at B, Fig. 33, so that when 
light source X is 
at the point where 
X and Y are equi- 
distant from the 
lens, as at A, and 
light source X and 
the lens are in the 
same relative posi- 
tion at B, point Y 
is much nearer the 
lens. The lens 
shown at A is a 
"long focal length" 
lens, and the one 
shown at B a "short 
focal length" lens, 
therefore you will 
observe that the Figure 34. 

heavier the curva- 
ture of the glass the shorter the focal length of the lens (the 
refractive index being equal) ; this by reason of the fact that 

the heavier the curva- 
ture the greater will be 
the angle at which the 
light rays strike the 
glass, hence the greater 
the amount of its re- 
fraction, and the nearer 
to the lens they will 

The surface of lenses 
used for projection 
work is always a sec- 
tion of the surface of 
a true sphere. In Fig. 
34 we see how the cur- 
vature of an ordinary 
Figure 35. plano-convex lens is de- 

termined. Assuming the 

outer circle to represent a glass ball ly?. inches in diameter, if 
you scribe on its surface a circle 4 l /2 inches in diameter and 
then saw off the section so outlined and polish its flat side, you 


would have a 7^2-inch plano-convex lens. If the glass ball repre- 
sented by the inner circle was 6 l /2 inches in diameter, then a 
similar operation on the surface of that ball would produce a 
6^2-inch plano-convex lens. But a lens may have two curved 
surfaces, as, for instance, a meniscus, and the method of deter- 
mining these surfaces is shown in Fig. 35, in which the two 
circles are made of a size to produce two surfaces which will give 
the effect desired, section X representing the resultant lens, 
which will have a convex surface on one side and a concave 
on the other. This is what is known as a "meniscus" lens. 
Its convex side is the "positive" and its concave side the 
"negative." In the lenses dealt with in Fig. 34, the inner 
or 6^2-inch lens would be 6^-inch lens because it would 
focus parallel rays of light at a point 6^ inches from its 
optical center. On the other hand the lens cut from the 
outer circle would be a 7 I />-inch lens, because it would focus 
parallel rays to form an image at a point 7^2 inches away; 
that is to say, it would do so theoretically. As a matter of 
fact, however, this is not precisely true, due to the fact that 
an uncorrected lens brings some rays to a focus nearer its 
surface than others. 

Spherical aberration in the condenser is governed by the 
fact that when parallel rays strike a plano-convex lens on the 
curved side the spherical aberration is reduced to a minimum, 
but if the rays be diverging, then the spherical aberration 
is less if they strike the piano side. This, of course, means 
that to secure the least spherical aberration the flat side of 
the rear lens must be next the arc where the rays are diverg- 
ing, and the convex side of the front lens must be toward 
the arc, since it receives approximately parallel rays from the 
rear lens. I mention this because some operators, though 
few, have a notion that they gain advantage by placing the 
curved side of the front lens next the machine aperture. This 
is an error. In fact, the actuality is the reverse, although but 
for the element of spherical aberration there would be little if 
any difference which way the lens was placed. 

In order to actually focus the rays of light perfectly the lens 
must be "corrected" by the addition of one or more lenses having 
negative curvature. 

As a matter of fact, the surface of a lens is really nothing 
more or less than millions of pin-points, each in effect a prism of 
minute dimensions. It is a well known fact that what we 
term "white light" is really composed of a number of colors. 
When white light, or what we call white light, is passed through 
a prism of glass, it is more or less separated into its primary 


colors, or, in other words, the colors of which it is composed. 
The ordinary plano-convex is an uncorrected lens, and always 
carries the fault of chromatic aberration, which is the property 
of separating light more or less completely into its component 
parts or colors. This explains why you see a fringe of color 
at the edge of the spot on the cooling plate of the machine. 

Now, taking the condensing lens for example, it being an 
uncorrected lens, remembering that, as I have said, its surface 
is composed of numberless minute prisms, you will readily see 
that the further away from the center of the lens you go the 
more acute will become the angle of these prisms with relation 
to the light source, or the light rays emanating from the source 
central with the optical axis of the lens, and therefore the more 
nearly true prism is approached. It then follows that, since the 
nearer we come to the true prism the greater will be the light 
separating power, we shall have a greater amount of chromatic 
aberration at the outer edge of the lens than at its center. Near 
the center of the lens the prisms will be very flat. Therefore 
their light-separating powers will be but slight; in fact, prac- 
tically nothing at all. At the outer edge these powers will be 
considerable, and here is where one of the evil effects of spherical 
aberration as applied to projection makes itself apparent. 

As already set forth, light rays near the outer edge of a lens 
will focus somewhat nearer the surface of the lens than will rays 
from near its center. This means that the excessive chromatic 
aberration at the outer edge of the lens is mingled with the 
purer light coming through the center of the lens, and the 
quality of the whole is thus injured. This is one of the reasons 
for my belief that there is advantage in the properly matched 
meniscus-bi-convex condenser combination. The addition of 
the negative curvature in the meniscus and the extra curvature 
in the bi-convex makes, in effect, a three and I believe a four 
lens combination, which has or ought to have to a considerable 
extent the effect of correcting spherical aberration. I do not 
state this as a positive fact. It has not yet been proven to my 
entire satisfaction, but I nevertheless believe it to be correct. 
There is, however, another decided advantage in the use of the 
meniscus lens next the arc, viz. : with a lens of given focal 
length the arc will be nearer the meniscus than it would be 
to a piano, hence a much greater amount of light will be 
transmitted to the screen. 

It is also possible that a condensing lens with a poor, im- 
perfect surface would have a considerable effect in injuring 
the definition of the picture. This seems to be made apparent 
in Fig. 51, which is a photograph of the light ray from a con- 


denser covered with a metal plate in which about a dozen 
quarter-inch holes have been drilled at various points. 

This photograph proves conclusively that a light ray passing 
through any given point of the condenser is carried forward to 
the screen, where it occupies a corresponding and magnified 
area. This being true, I cannot see but that any imperfection 
in the condensing lens which would in the least tend to alter 
the direction of a ray from the path it would have taken were . 
the lens a perfect lens must of necessity injure the result on 
the screen, though Mr. Griffiths does not agree with this con- 
clusion. However, I do not care to go deeply into this matter 
at this time, not being entirely sure of my ground. 

The operator will have noted the fact that when the machine 
head is removed, and the white light projected to the screen 
without any objective lens, it is impossible to bring the light 
ray, as a whole, to a sharp point. Most operators have hereto- 
fore believed that the rays from the condenser were supposed 
to meet at a point and cross midway between the front and 
back factors of the objective lens. This is not true. See Page 118. 
The condenser does not bring the light ray as a whole to a 
point. It forms an image of the crater, and upon the size of the 
image thus formed will depend the diameter of the condenser 
light ray at its narrowest point. It is a mistaken idea to suppose 
that when we speak of a lens "focusing the rays" we mean that 
it brings the ray, as a whole, to a sharp point. It does not. What 
is really meant is illustrated in Fig. 32. All light rays emanating 
from any pinpoint of objective X and reaching the surface of 
the lens are refocused at a similar point in image Y. This 
image may be smaller than the original object. Study Fig. 
32, and I think you will get the idea. 

The Objective. The objective lens of the moving picture 
projection machine consists of four lenses, two in the rear fac- 
tor and two in the front factor. The two at the front are 
usually cemented together with Canadian balsam, so that, at a 
superficial glance, they appear to be one thick lens. As a 
matter of fact it is one thick lens, with a thin one cemented 
to the front so that the surfaces of the two lenses are brought 
into contact. It sometimes happens that the heat will melt the 
balsam and cause it to run down between the lenses. When 
this happens it is best not to try to fix it yourself, but send the 
lens back to the manufacturer to be recemented. However, you 
can separate the lenses (though I do not advise you to try it) by 
proceeding as follows : Set a shallow dish, filled with water, on 



the stove, place the lens on a large kitchen spoon or tablespoon 
and set the spoon in the water, so that the lens will be covered. 
Allow the water to come to a boil and remove the lens quickly, 
shoving with your thumbs on one lens and pulling with your 
fingers on the other. It is a pretty hot job, and you will have 
to use considerable force, but if you bring the water to a boil 
it softens the balsam and you can get the lenses apart. The 
balsam can then be washed off with turpentine. 

Distortion. Operators should carefully test their objective 
lenses for distortion. This may best be done by taking a per- 
fectly flat piece of mica, commonly known as isinglass, three 
or four inches long, and cutting it to the width of a film. Hav- 
ing done this, lay it off checkerboard fashion, as per Fig. 36, 
and put it in the machine, being careful to get it perfectly flat 

Figure 36. 


over the aperture, and project its image to the screen. At A, 
Fig. 36, we see no distortion. At B there is what is known 
as barrel distortion, which amounts to a curvature of the lines. 
The lens which projects B is not a good lens, whereas the lens 
which projects A is practically perfect. The scratch marks on 
the mica may be made with the point of a knife blade, or any 
other sharp instrument. The lines on the mica must be perfectly 
straight, and if their image on the screen is not perfectly 
straight (test by streching a line) the lens is imperfect. 

A lens must focus all light rays passing through a pinpoint 
in the photograph to a corresponding though magnified point 
on the screen. The distance at which this focusing will be 
accomplished depends, within limits, upon the distance of the 
film from the lens the back focus at which the lens is working. 


This is diagrammatically illustrated in Fig. 37, in which arrow 
A is being projected and focused at point 1. That is to say : 
With the arrow at the distance from the lens, as shown, the 
rays will meet and cross at point 1, where they begin to diverge. 
If the screen be placed at point 2, arrow A remaining its 
original distance from the lens, instead of an image on the 
screen, each portion of arrow A will be represented by a 
blurred ring. If the distance of arrow A from lens B is altered, 

then the distance at 
which the rays meet 
and cross (image) 
will be altered, and 
the screen will have 
to be moved toward 
or from the lens 
a corresponding dis- 
tance. This explains 
Figure 37. why it is necessary 

to move the lens in 

and out in order to focus the picture on the screen. Where 
the back focus is short, as in a moving picture lens, a slight 
alteration of the distance between the lens and the film makes 
a decided difference in the distance at which the rays of light 
will focus. 

Doctoring Lenses. The question is often asked: "Can the 
E. F. of a lens be altered by shortening or lengthening the 
barrel, so as to alter the distance between its two factors?" 
Yes, but it is not advisable to try anything of that sort. The 
chances are that you will ruin your lens. This scheme has 
been known to work fairly well in some instances, but more 
often than not it is more or less of a complete failure. 

Bringing the two" combinations closer together or separating 
them farther apart would have the effect of altering the size 
of the picture on the screen at a given distance, but it is a very 
poor way of doing it. 

The author has frequently been asked whether or not the 
same lenses may be used to project a picture at different dis- 
tances. Yes. But it must be understood that if the distance be 
made less, then the picture will be smaller, and if the distance be 
made greater the picture will be larger. Also moving the 
screen will alter the back focus at which the lens will work. 
The shorter the distance between the lens and screen the farther 
the lens must be from the film, and vice versa. 


Spread of Ray. It is easy to figure how much change in 
size of picture will be accomplished by moving the screen any 
given distance. Suppose you have a lens which projects a 10-foot 
picture at 60 feet. It is readily seen that if the width of the 
picture be divided by the number of feet it is projected the 
result will be the fraction of a foot its width increases with 
each foot of distance, hence in this case we have 10 -f- 60 = one- 
sixth of a foot, or 2 inches, which is the amount the light ray 
spreads for each foot of distance between the lens and screen. 
In proof of this, multiply 2 X 60 and we have 120 inches, or 10 
feet. Now, if you move your screen back five feet farther 
you will have 2 X 5 = 10 inches additional width of picture, or 
if we brought the screen 6 feet nearer the lens, then we would 
have 2 X 6 = 12 inches less width of picture. 

Improving Definition. The work of a projection lens which 
does not give sharp definition may sometimes be improved by 
cutting a circle of stiff dark paper, just large enough to fit 
tightly into the front end of the lens barrel and up against the 
front lens. In the center of this ring cut a circular opening, 
the correct size of which must be determined by experiment in 
each individual case. Usually it is not advisable to stop down 
more than one-fourth the diameter of the opening. This is 
often of benefit in sharpening the focus where the machine sets 
above or to one side of the screen, because reducing the lens 
diameter has the effect of increasing its depth of focus. 

Dirty Lenses. It is of the utmost importance that the 
operator keep his lenses scrupulously clean. "Optical Projec- 
tion," by Simon Henry and Henry Phelps Gage, gives the losses 
by reflection from the polished surface of each surface to each 
lens as from 4 to 5 per cent., or a total of 8 to 10 per cent, for 
each lens or plate of glass, and further remarks that if the 
surface of the glass be not perfectly clean or perfectly polished 
the light loss may amount to much more say 15 per cent, at 
each surface. 

It really seems to me that this cannot be true. There being 
eight surfaces in an objective lens, or since two of them are 
in direct contact, let us say six, even taking the lowest figure, 
viz., 4 per cent, for each surface, we would have a total of 
24 per cent, loss by reflection alone. However, without dis- 
cussing the probable correctness of the percentages, it is an 
undoubted fact that there is considerable loss through reflec- 
tion, and this loss will be very largely increased if the lens be 
dirty. Therefore, it is very much up to the operator to keep 
his lenses not only clean but polished as highly as possible, 


Measuring Lenses is a very simple operation. In order 

properly to match up a projector lens system it is necessary 
that the operator be able to measure and determine the exact 
focal length of his condenser lenses, and it is often very desirable 
that he be able to measure the exact equivalent focus of an 
objective in order that he may determine what size picture it 
will project at a given distance. 

Plano-convex lenses may be measured as follows: Pin a 
sheet of white paper to the wall of a room, opposite a window, 
hold the lens up with its flat side toward the wall and, through 
the open window, carefully focus some building, trees, or other 
object located at a considerable distance outside the window, 
on the paper screen. It is essential to accuracy that the object 
being focused be a goodly distance away the farther the better 
because in these measurements the light rays are presumed 
to enter the lens in parallel lines, and unless they do enter in 
approximately parallel lines there will be error in the result. 
Be sure to get the lens in exact position where the focus of the 
image on the paper screen is most sharp, and then measure from 
the flat side of the lens to the wall, making a note of the pre- 
cise distance. Next turn the lens around and with the convex 
side toward the wall, again carefully focus the same object 
on the paper screen and measure from the wall to the flat side 
of the lens. It will be found that the two measurements will 
differ considerably, and their sum divided by 2 will be the focal 
length of the lens. For instance: Suppose one measurement to 
be 6 inches and the other 7 inches : 6 + 7 = 13 which divided 
by 2 = 6H> therefore it is a 6 l / 2 inch lens. 

It is not practical to measure condensing lenses with any 
great degree of accuracy. There is so much spherical aberra- 
tion in these uncorrected, comparatively cheap lenses, that the 
picture cannot be focused with absolute sharpness. The focal 
length of the lens may, however, be arrived at by the fore- 
going process closely enough to serve all practical purposes. 

The measuring of a motion picture objective or stereopticon 
lens is a very simple operation. The focus of a projection 
lens may be designated in two ways viz., back focus (common- 
ly expressed as b. f.) which is the measurement often used by 
the film exchange, and equivalent focus (commonly expressed 
as e. f.), which is the measurement used by the lens manufac- 
turer. Therefore in ordering lenses of a given focal length 
one should be careful to state whether the measurement given 
represents b. f. or e. f. The e. f. is the measurement which must 
be used in ordering lenses to project a picture of given distance. 


To measure a moving picture objective or stereopticon lens 
pin a sheet of white paper to a wall opposite a window. Hold 
the lens square with the paper screen and, through the open 
window, focus some building, tree, or other distant object on 
the paper screen; be very careful to get the image as sharp as 
you possibly can. Now measure from the wall to the surface 
of the lens nearest the screen, and that measurement will be 
the back focus, or b. f. of the lens. If, instead of measuring 
from the surface of the lens to the screen, you measure from a 
point half way between the front and back combinations of the 
lens (half way between the lenses at either end of the tube) to 
the paper screen, that measurement will be the equivalent focus, 

I i 


i r M 1 1 1 1 1 < i ' i ' i > i ' i ' i > i ' i M 1 1 

Figure 38. 

or e. f. of the lens. In other words. the e. f. is equal to the b. f. 
plus half the distance between the two combinations of the lens. 
All this we see diagrammatically represented in Fig. 38. 

Again let me caution you always to focus some DISTANT object; 
an object which is 100 feet away will do, and even an object 25 
feet away will not be close enough to affect the result very 
much. It is even possible to get an approximate measurement by 
focusing an incandescent light, provided it be at least 10 or 15 
feet away, but such a measurement cannot be depended upon 
when accuracy is essential. Also see Page 108. 

The use of these measurements, as applied to the objective, 
becomes apparent when we learn that the size of the picture 
which will be projected by any lens at a given distance from 
the screen will be entirely dependent upon the focal length of 
the lens. The shorter its focal length the larger will be the 


picture at a given distance, and the longer its focal length the 
smaller will be the picture at a given distance. A lens having 
a 4-inch e. f. will project a much larger picture at 50 feet than 
will a lens having a 6-inch e. f. 

Nearly all machine and lens manufacturers put out tables de- 
signed to tell one the exact size (width) picture a lens of given 
focal length will project at a given distance. These tables are 
useful as applied to stereopticon lenses, but have slight value 
as applied to the moving picture objective this by reason of 
the fact that the size of picture is based upon a given width of 
aperture, which, in the case of the stereo, is supposed to be 3 
inches, but which may vary widely with each set of slides 
(the aperture in the case of the stereopticon is the width of 
the standard slide mat) ; hence, by reason of the variation in 
the size of slide mats it is impossible to figure the size of a 
stereopticon picture with any degree of accuracy, and the table 
will therefore answer about as well as measurements. 

As applied to the motion picture objective, however, these 
tables are not at all satisfactory. As a rule operators and man- 
agers want their picture not approximately, but exactly a given 
width. Now there are at the present time two different stand- 
ards of motion picture machine aperture widths, viz., 15/16 and 
29/32; also the aperture of the older machines of different 
makes, while they were presumed to be all 15/16 of an inch, 
really varied considerably, and a slight variation would make 
.considerable difference in the size of the picture on the screen, 
as for instance, if you used 15/16 of an inch as a basis for 
figuring, and the aperture really was a little more or a little less 
than that width, then the result would be a picture wider or 
narrower than your figures called for. This being the con- 
dition, you can readily see that tables cannot be depended upon 
for any very great degree of accuracy in results.. I will, how- 
ever, for reasons already set forth, append one of the tables 
for stereopticon lenses. 

To figure the necessary equivalent focus of a lens to project 
a picture of given width at a given distance proceed as follows : 
Have a machinist measure the aperture of your machine ac- 
curately with an inside caliper and a micrometer. Measure the 
exact distance from the lens to the screen. Multiply the dis- 
tance from the lens to the screen, in feet, by the width of the 
aperture, in fractions of an inch, and divide the result by the 
width of the picture you desire, in feet. The result will be the 
c. f. of the lens required to project a picture that width, and will 
be as close to it as you can get at it by figuring. For instance : 
Suppose you want a 15-foot picture at 60 feet, The machine 


aperture is found to be 29/32 of an inch (the new standard) 
wide. First multiply the distance from the screen in feet by 
the width of the aperture in fractions of an inch. To multiply 
60 by 29/32 we first divide by 32 and multiply the result by 29 ; 
60-7-321.875; 1.875X29=54.375. Next we divide this 
measurement by the desired width of picture in feet: 54.375 -^ 15 
= 3.625, or a 3^?-inch e. f. lens. We most likely would be un- 
able to get that exact focal length and would have to take, in- 
stead, a 524-inch e. f. lens. 

It must be understood, however, that the great bulk of pro- 
jection lenses now in use are cheap lenses, and cheap lenses, 
like all other cheap things, are inaccurate, therefore you can- 
not expect to arrive with certainty at precisely the result you 
desire in any other way than by actually testing the lenses. 

The stereopticon lens is figured exactly the same way, except 
that instead of measuring the aperture width, we take 3 inches 
as the average width of the slide mat the slide mat, in this 
case, being the aperture. 

It is also entirely practical to make other measurements of 
practical value as follows: Suppose you have an objective and 
wish to know what size picture it will project at a given dis- 
tance. First measure its e. f. as already directed and then: 

Size of Image. This can be determined by multiplying the 
difference between the distance from lens to screen and the 
focal length of the objective, by the width of the aperture and 
dividing the pro-rlurt by the focal length of the lens. For ex- 
ample: Let L be the projection distance, 40 feet (480 inches); 
S, the slide mat, 3 inches; F the e. f. of the lens, 12 inches; 
we then have the formula (in which d is the size of image) ; 

S (L-F) 


Substituting for the letters their known values, we have: 
3 (48012) 

=117 in., or 9^ feet, 


as the size picture a 12-inch e. f. stereo lens will project at 40 
feet, provided the slide mat be just 3 inches wide. If. how- 
ever, the mat be more or less than 3 inches, then the picture 
will be wider or less wide. 

Distance from Slide to Screen. With the other factors 
given we get this by multiplying the sum of the width of the 



Showing Size of Screen Image When Lantern Slides 
Are Projected 

Size of Mat Opening, 2^x3 Inches 
Table 7, Figure 39 

Equlv. focus 























































































































































































































































































if. 4 














































EXAMPLE: With a lens of 10-inch focus at a distance of 
20 ft. the screen image will be 5.3 x 5.8; at 25 ft., 6.6 x 7.3; 
at 30 ft., 8.0 x 8.8; at 50 ft., 13.5 x 14.8 etc. 


image and width of the slide mat, by the focal length of the 
lens ; dividing this product by the width of the slide mat, thus : 

F(d + S) 

T _ ________ 

12(117 + 3) 

Substituting values, L = 480 inches = 40 feet. 


Measuring E. F. Accurately. Should the operator desire 
to measure the e. f. of his objective with absolute accuracy 
he may proceed as follows: Remove the mechanism and in 
the position the aperture of the machine occupied place a 
sheet of tin having an aperture about three-quarters of an 
inch square. Now hold the lens out at a distances about 
twice the length of its supposed e. f., in front of the aperture, 
with the light turned on, and an equal distance in front of 
the lens (still further out) hold a small screen, preferably 
dull black in color, and move the lens and the screen until 
the image of the aperture on the screen is exactly the same 
width as the actual aperture. Now measure the distance from 
the aperture to the screen and divide it by 4; the result will 
be the exact e. f. of the lens. 

Cleaning Lenses. It is of the utmost importance that 
lenses be kept scrupulously clean. Oil and fingermarks are 
particularly objectionable. I have been called to theaters 
to locate the cause of lack of sharp focus in the picture, only 
to find that the operator had had his objective apart to clean, 
and in putting it together had inadvertently lightly touched 
one of the interior surfaces of the lens with his finger. The 
mark was so slight that it could not be detected by looking 
through the lens, but was quite visible when the lens was 
taken apart and looked at from an angle. Slight as this mark 
was it seriously injured the definition of the picture. 

Oil on the surface of a lens will also operate to injure the 
focus of the picture. I do not think any argument is neces- 
sary on this particular point. 

It is absolutely essential to sharp definition of the picture on 
the screen that all lenses be kept scrupulously clean. 

The careful painstaking operator, whose machines run several 
hours each day, will clean his condensing lenses every day, par- 
ticularly the one next the arc. The objective lens need not 
be cleaned more than perhaps once a week, unless oil spatters 
on its rear surface, in which case it should be cleaned just 
as soon thereafter as possible, and if there is tendency of oil 


to spatter on the lens its rear end should be protected by 
some kind of a metal guard. I cannot tell you just now how 
to do this, because the method would vary with different 
mechanisms, but certainly the competent operator can devise 
ways and means to keep the oil off the rear end of his lens. 
In some cases a collar of tin made tight enough to clamp the 
rear end of the lens barrel, extending back nearly to the 
aperture, will answer the purpose. 

Unless there is oil on the lens I know of no better way of 
cleaning them than by breathing on the cold glass and polish- 
ing with a perfectly cle n chamois, or an old, clean, soft 
handkerchief. Always provided there be no oil present, this 
t will clean the surface of the lens perfectly, and will answer 
every purpose. If there be oil on the lens, then I recom- 
mend the use of a solution of one half alcohol and one half 
water. Wash the lens off with a cloth saturated with the 
solution, and polish quickly with a dry, soft, clean hand- 
kerchief, perferably an old one. Nothing makes a better lens 
cloth than an old, worn out handkerchief, after having been 
laundered. Some operators prefer a solution of ammonia and 
water or water and alcohol. 

The operator should, perhaps twice a year, take his ob- 
jective lenses apart and clean their interior surfaces, being 
very, very careful that in putting them back he does not 
touch their surface with his fingers. This latter is of the 
utmost importance, because the very lightest touch will leave 
a mark which, while invisible when looking through the lens, 
is likely to seriously injure its work. In replacing the ob- 
jective lens factors always put them together so that the 
heavy bulge or convex of all lenses is toward the screen. 
In taking out the rear combination be careful that you put 
them back in the same position they were in. In other 
words, don't get their position switched. The best way to 
go about this is to lay a sheet of paper on a table and write 
"rear lens," "inside lens," and "front lens," at different places 
on its surface. Now as you take the lenses out lay the rear 
one (next the aperture) on the space marked "rear lens," 
the inside one on the next space, and the front on the space 
marked "front lens." Then you cannot very well make any 
mistake. You will find a spacing ring between the two rear 
lenses. Be sure and get it back in its place when you put 
the lenses together. 

Fig. 40| shows the position of the lenses in an objective. 
The two front lenses are cemented together with Canadian 
balsam. (See Page 100.) 



Selecting Condensing Lenses. See Page 127. 

Lens Diameter. Lens diameter is a subject of much im- 
portance. With a point source of light it would be quite 
impossible to use a very small diameter and place the arc 
right up close to it. Modern practice, however, is to use an 
amperage for the projeection of moving pictures which pro- 
duces a crater varying from (D. C.) one-quarter to one-half 
inch in diameter. This, of course, means a light source of 
very high temperature, and more or less naming of the car- 
bons, so that the light source cannot be brought very close 
to the lens. So far as the condenser be concerned, as a rule 
the diameter of the lens next 
the arc might be 4 inches as 
against a 4%-inch diameter 
for the rear lens without in- 
creasing light loss; this by 
reason of the fact that the 
condenser next the arc 
usually, with the arc in oper- 
ating position, produces a 
diverging ray beyond the 
lens, and it is only necessary 
that the front lens have suf- 
ficient diameter so that the 

light from it will just cover the front lens. This is not intended 
to mean that the author expects any change of this kind will 
be made. It is simply an interesting point, though in Eng- 
land and Germany use is made of a lens next the arc which 
has a smaller diameter than the front lens. Four and a half 
inches seems to be fairly satisfactory diameters for con- 
densers. Whether there would be, considering the proposi- 
tion as a whole, any gain in using a larger diameter con- 
denser I am not quite sure, but doubt it. 

The diameter of the objective lens is a matter of the utmost 
importance. See Page 121 and Fig. 49. 

High-Grade Lenses. The author of this work is thoroughly 
and completely convinced that it is a tremendous mistake 
to use cheap objective lenses for projecting the picture. This 
most emphatically is not the result of snap-shot judgment, 
but a conviction which has been growing for some years 
which was finally clinched by knowledge of the fact that the 
better English theaters are using lenses costing as much as 
12 (approximately $60), supplemented by absolute proof 
that there is a very large possible gain in illumination 
and sharpness of focus by using a high class objective lens. 

Figure 40. 


The projection of the picture is nothing more or less than 
a reversal of the process of its photographing. Film manu- 
facturers spare no expense in procuring the best lens obtain- 
able for their cameras. These lenses are a magnificent ex- 
ample of the optician's art. They must have great "depth" 
and plenty of "speed." They must be corrected for about 
every imaginable fault, and the result is that they register 
on the film a wealth of detail, depth, and sharpness which 
are largely lost by reason of the fact that the photograph 
must be projected by about the cheapest lens it is possible 
to obtain. 

Authorities in England, where] they have already made 
considerable progress in the high-grade projection lens 
business, claim that in order to get a perfectly flat field it is 
necessary that an anastigmat lens be used. I cannot vouch 
for the correctness of this, but am told by lens men here in 
America that it is true. 

These same authorities who have experimented with ihigh- 
class objectives for the projection of pictures claim that 
the high-class lens will pay its additional cost within a com- 
paratively short time in current saving, it being the fact that 
these lenses give a greater illumination per ampere of cur- 
rent than do the ordinary objectives now being used. This 
I personally have seen demonstrated. 

Just reason with yourself for a moment. If the cheap leni 
is the right thing with which to project a picture, then why 
is it not the proper thing to take the picture with? Why 
take a picture with a costly, high-class lens and project it 
with a cheap, comparatively poor article. It doesn't sound 
like common sense, does it, gentlemen? 

I notice that no less a person than Simon Henry Gage, 
Cornell University, a man deeply versed in the science of 
optics, in his work on "Optic Projection," says there is no 
particular value in having a perfectly sharp picture if it is 
to be viewed at a considerable distance. He even says a 
little coarseness is an advantage. With this I cannot at all 
agree. I have the utmost respect for the knowledge of 
Professor Gage, but in this one particular thing I think 
he is decidedly in error, and, moreover, assuming he is right, 
it must be remembered that a goodly portion of the audience 
is seated compartively near the screen. 

The writer makes no claim to being an expert in lenses 
far from it. He does, however, claim to be the possessor 
of a considerable fund of common sense, and common sense 
tells him that the sharper the picture is the better for all 



concerned. Moreover, flatness of field is to be highly de- 
sired, since curvature of field means there will be a tendency 
to out-of-focus effect at the edges when the center is in 
focus, and vice versa. This may or may not be sufficient to 
be noticeable, but is apt to be very much so with short focal 
length lenses. It is in the nature of things, and cannot be 
otherwise unless the lens is corrected to produce a flat field, 
and as I understand it that means an anastigmat lens. 

I would strongly advise theatre managers to purchase high- 
class lenses for their projectors. I would even advise them 
to have no hesitation in paying as much as sixty dollars for 
a good lens. The Kleine Optical Company, Chicago, is 
handling high-grade lenses. The Dallmyer lenses are handled 
by Burke & Jones, New York City and Chicago, and the 
other European manufacturers producing high-class pro- 
jection lenses also have their representatives in this country. 

Just at present it may be difficult to secure just the right 
kind of lens, but I have had proof of the fact that the lenses 
handled by Mr. Kleine, listed from thirty to sixty dollars, are 
a very good article, and worth every cent of their price. 


In order to insure the best possible results on the screen 
it is essential that the light source (crater), the optical axis 
of both condensing lenses, and the optical axis of both com- 
binations of the objective be exactly in line and square with 

Figure 41. 

each other, and that a line drawn through the optical axis of 
the lens system shall pass precisely through the center of 
the aperture of the projector. 


In Fig. 41, A is the crater, B the lamphouse condenser 
opening with the condensers removed, D the aperture of 
the projector, E the objective lens barrel, with the lenses re- 
moved, and F the opening in the wall of the operating room. 
H is a stand of white sewing thread or a fine copper wire, 
G is a light metal rod placed across the opening in the opera- 
ting room wall, and supported by string H being drawn taut 
The method of procedure is as follows: First remove the 
condensing lenses and remove the lens factors from the 
objective, but leave the barrel screwed firmly in its place 
in the lens ring. Next attach cord or wire H to rod G, and 
pass the cord or wire through the lens barrel and machine 
aperture, as shown, and bring it back and tie it around the 
point of the upper carbon. After all is ready pull the lamp 
back by its forward and backward adjustment (before 
beginning it should be shoved clear ahead) until string or 
wire H is pulled tight just tight enough so that rod G- will 
be held in place and the string or wire be perfectly straight. 
Now with caliper C carefully center cord or .wire H in con- 
denser opening B, machine aperture A, and both ends of 
objective lens barrel E, moving whatever may be necessary 
to accomplish the purpose. I cannot tell you what you will 
have to do to get the string in the center since this will vary 
in different cases : it will have to be left to your ingenuity. 

No attention should be paid to hole F in the wall as that 
has nothing whatever to do with the lining except to sup- 
port rod G which holds the string in place. The fastening 
of the cord to the carbon point will be facilitated by using 
a three cornered file and filing a small notch at N. 

Matching Up the Lens System 

THE action of light rays through a projection system 
has been the subject of mudh controversy, and I 
believe it might fairly be said that until the pro- 
jection Department of the Moving Picture World undertook 
a series of experiments and went into an exhaustive study 
of the matter, no very intelligent explanation of the action 
of light rays through the projector system had ever been 
promulgated that is to say, no explanation which "squared 
up" with what apparently actually took place. 

The main stumbling block in this proposition lay in the 
fact that the same conditions do not obtain in the projection 
of moving pictures that obtain in stereopticon projection; a 


fact which opticians have failed to observe, attacking the 
problem of projecting moving pictures from the same stand- 
point as of projection lantern slides. The difference in the 
two problems lies in the following: In stereopticon projec- 
tion the object (slide) is situated right up against the con- 
densing lens, whereas in moving picture projection the ob- 
ject (film), is at, or near the crater image a foot or more 
away from the condenser, and at one of the conjugate foci 
points of the condenser system. This means that the two 
problems present very different angles. In order to obtain 
maximum illumination in stereopticon projection the crater 
image must 'be approximately central between the two factors 
of the stereopticon objective lens, whereas in moving picture 
projection it must be at or near the object (film). 

The author does not believe this matter to be, as yet, 
entirely solved, but he does believe that great progress 

Plate 1, Figure 42. 

has been made, and that the tables representing that progress 
which are hereto appended will be found to be approx- 
imately correct, and that they will, barring the limits imposed 
by present day apparatus, enable the operator to match up 
his projector lenses in a way to give very satisfactory results. 
In this connection we are especially indebted to John 
Griffiths, Ansonia, Conn.; W. S. James, formerly of Camden, 
N. J.; C. D. Armstrong, Ashland, Wis.; and L. C. LaGrow, 
Albany, N. Y. These men have aided very greatly in the 
solving of this difficult problem and Griffiths has contributed 
the greater portion of the theory upon which the tables are 
based, as well as worked out the tables themselves. 



The Condenser. The spacing of the two condenser lenses 
different distances apart has the effect of altering the 
equivalent focus of the combination. The further the lenses 
are spaced apart the longer will be the E. F. of the combination, 
and vice versa. 

It seems, however, that, in view of the fact that with the 
arc at ordinary operating distance from the rear condenser 
lens, the light ray di- 
verges after passing 
through the rear lens 
(see A-B, Plate 1) and 
that, incidently, this 
divergence increases with 
increased focal length of 
the rear lens, it is ad- 
visable that the condens- 
ing lenses be placed as 
close as possible to each 
other (without actual 
mechanical contact, which 
latter would tend to con- 

vey heat to the front P^te 2, Figure 43. 

lens), since the further apart the lenses are the greater must be 
the loss through the aforesaid divergence of the light ray. 
A and B, Plate 1, show a 6 l /z and a 7 l / 2 lens, with the arc 
the same distance from the lens, using equal amperage in 

both cases. Even with 
the lenses set so that 
their curved surfaces are 
within one-sixteenth of 
an inch of each other 
there will still be some 
loss, but this cannot be 
avoided, since if we pull 
the arc back far enough 
to bring the light rays 
parallel after passing 
through the front lens, 

Plate 3, Figure 44. t ^ ien we w ^ encounter 

still greater loss on the 

arc side of the lens, by reason of increased distance between 
the arc and the lens and the law that intensity of illumination 
decreases inversely with the square of the distance from the 
light source. 



Plates 2 and 3 illustrate the relative loss through spacing 
of the lenses, Plate 2 shows the lenses set with their curved 
surfaces approximately one-sixteenth of an inch apart. 
Plate 3 shows the lenses spaced so that their curved 
surfaces are one-half inch apart. It will be observed that 
the loss of light is materially greater in Plate 3 than in 
Plate 2. 

It is also of interest to note the difference in the light 
beam itself. In Plate 2 the beam does not narrow down quite 
so much as it does in Plate 3, and the crossing point of the 

Diagram showing how the back focus and the size of the aperture of the 
objective lens determine the distance between condensers and anerture. 

20 19 

15 14 13 12 II 10 9 8 
Distance between condensers and aperture when the buck focus of 

Plate 4, Figure 45. 

rays is much nearer to the lens, which means that the E. F. 
of the combination has been lengthened by spacing the 
lenses. However, due to reasons already set forth I believe 
it is better practice to work with a fixed E. F. y setting the 
condensing lenses so that their curved surfaces are not more 
than one-sixteenth of an inch to one-eighth of an inch apart, 
and make other conditions fit this one. 

Never have the lenses actually touching each other, since 
mechanical contact would serve to impart considerable heat 
to the front lens, which is decidedly undesirable. 



The novice would probably say that, since the light cone 
is shorter in Plate 3 than in Plate 2, the E. F. of the Plate 3 
combination would be less. The opposite is true, however, 
Measurement from a point half way between the two lenses 
to the point where the rays begin to diverge from the main 
beam will show that the cone is shorter in Plate 2 than in 
Plate 3. 

It may be stated as an absolute fact that when the con- 
denser is made up of two factors of different focal lengths, 
as for instance, a 6 l / 2 and a 7 l / 2 lens, the better practice is to 

Showing how the 
objective is covered 
by the incident light 
when the directions 
given in the tables 
are followed. 


Tmhies-back focus 
of objective lens. 



NOTE. Line A would pass from the extreme edge of 
the conuenser to the extreme edge of the objective 
lens and just pass through the narrowest part of the 
machine aperture. Line B goes from the opposite 
extreme edge of the condenser to the opposite extreme 
edge of the objective. And while these two rays form 
an internal part of the condenser beam of light they 
form the extreme rays of the beam after passing the 

place the shorter focal length lens next the arc. This is 
proven by A-B, Plate 1. The only objection to so doing is 
that the thick lens is more apt to break than is the thinner 
one, but this may be very largely if not entirely overcome 
by the installation of a modern condenser mount, of which 
the Elbert or Preddy (see index) are excellent examples. 

In the course of the aforementioned experiment's it has 
been proven to the author's entire satisfaction that, provided 
the front lens of the condenser combination be in line with 
and square with the aperture and objective, the fact that the 


rear condensing lens it not exactly square or in line with the 
front one does not make any serious difference, provided, 
of course, that the fault be not too great. I do not wish to 
be understood as saying that this condition ought to be 
allowed to obtain. The better practice is to have the entire 
lens system in exact line, but with present projector mounts 
this is ,a somewhat diffcult thing to accomplish, and failure 
to accomplish the lining of the two condenser factors per- 
fectly with each other will not be a very serious matter. 

Another extremely important relation between the con- 
densing lens and the objective is illustrated in Plate 4, in which 
A represents the extreme limit of light from the lower 
edge of the condensing lens when it is placed 16 inches from 
the aperture of the machine. You will observe that with 
the condenser at a distance from the aperture which will 
place the arc in focus (the point where the condenser ray 
begins to diverge), which is the point where the picture will 
receive evenly distributed illumination, the light will pass 
through the aperture and become a diverging beam. This 
is clearly shown in Plate 5, which shows the light beam as in 
actual projection, and is proven in Plate 6, in which the 
condenser is covered by a metal plate in which are two holes 
located diametrically opposite each other and about a half-inch 
from the edge of the lens. It will be seen from Plate 6 
that the rays from the outer edge of the condenser lens 
actually do act precisely as indicated in diagram, Plate 4. In 
Plate 7 the same two rays are passed on through the ob- 
jective lens. 

From this the inevitable conclusion is reached that, with the 
crater in focus at the aperture, the closer the condenser is to the 
aperture the more rapid will be the divergence of the beam 
beyond the aperture, though the increase from this will be 
comparativetly slight. It will also be seen that the greater the 
distance from the aperture plate to the objective lens aperture 
the wider the light beam will be at the point it encounters the 
lens, See Plate 8. It therefore is an undoubted fact that 
the diameter of the objective lens is an exceedingly im- 
portant factor, particularly with long focal length lenses, and 
it is a factor which must be taken into very serious account 
in the matching up of projector lens systems. 

Plate 9 shows the loss of light through using a lens of 
too small diameter. This loss may be slight; or it may be 
very great. In many cases it is the latter. In this case the 
loss is far greater than appears, because the camera only 
caught the loss which fell outside the lens barrel, whereas 




the actual diameter of the lens aperture is considerably 
less than the outside diameter of the barrel. 

In Plate 4, the long scale marks condenser distance, and the 
short scale, to the right, indicates the back focus of the 
objective. Any objective lens may work at any one of several 









different distances from the film. That is something I 
have never been able to make fit in with any plan I could 
evolve for matching up a projector lens system. Like most 
other things, however, once you get hold of the right key 


it is very simple, and the key to this particular problem is 
"back focus." 

In matching up a projector lens system, first, using the 
well-known formula for finding the equivalent focus of the 
lens required to project the size picture you want at the 
distance your condition calls for, determine the E. F. of 
the lens you want, procure it, mount it in the machine, and, 
using any condenser, project a picture, and very carefully 
adjust the objective until the picture on the scree'n is in 
sharp focus. Having done this, stick a rule through the 
aperture and, with its end against the lens, measure the 
exact distance of the rear surface of the rear combination of 
the objective from the film track surface on the aperture. 

This measurement will be the BACK FOCUS at which your 
lens will work, and it is this measurement and not the equiva- 
lent focus, which must be used in matching up the lens 
system. The E. F. has absolutely no value whatever except 
to enable the operator to select the proper lens to project 
the size picture he wants at the given distance. 

At this point we reach an item of much importance, con- 
cerning w/hich positive data cannot as yet be given, viz.: 
The selection of an objective lens of the right diameter to 
fit local conditions. Excess in diameter is undesirable, in 
that it is likely to set up trouble in the shape of travel 
ghost. Insufficient diameter, on the other hand, means loss 
of light, and loss of light is expensive. On the whole, it is 
much better, I believe, to get a lens of too large than too 
small diameter, because it is an easy matter to stop down the 
large lens to just the size needed, whereas the small diameter 
cannot possibly be made larger. 

On the whole, I think the best recommendation we can 
make at present is that the E. F. of the required lens be 
found, and that a lens be ordered having a diameter equal 
to one-half its E. F., up to 4^ inches E. F., the diameter beyond 
that focal length to remain fixed at 2% inches, up to 7 inches 
E. F., beyond which it might possibly be increased to 2^ inches 
with advantage. When the lens is received, place it in the 
machine and focus the picture sharply on the screen, then measure 
the back focus, as already directed, and remove the lens. Now 
place a sheet of white paper inside the mechanism in the exact 
position occupied by the back surface of the lens, supporting 
it in any convenient way, without Jiaving changed the position 
of the lamp with relation to the condenser or of the lamp- 
house with relation to the aperture, strike an arc, and measure 



the light on the paper. If the lens meas- 
ures 2 inches in diameter and the light 
measures 2 inches across, all is well. If 
the light measures more than 2 inches 
across, but only 2 inches up and down, the 
lens still will do fairly well, though there 
will be some loss. If, however, the lens 
measures greater than the light, stop the 
lens down to the diameter of the light at both 
ends, by means of rings of metal in which 
you have made a circular opening of proper 
size. I do not pretend to say that this 
advice is perfect. It is, however, the best I 
can offer at this time, and is, I am sure, 
based on the right idea. 

A Digression. Let me pause here, for 
T-; want of a more fitting place, and digress 
^J for a moment to show you an interesting 
light ray picture. 

.? In Plate 10 we see a condenser with a 
^ metal plate having a number of holes, each 
f about one-quarter inch in diameter. This 
o picture has no considerable value, except to 
allow the operator or student to trace the 
^ light ray action on both sides of the ob- 
jective. It will be noted that the screen 
illumination is not complete, especially at 
the outer edges where there were but few 
holes in the metal plate. Another interest- 
ing point in this picture is the circle of 
light on the back side of the aperture plate, 
showing the loss of light through reflection 
from the polished surface of the lens. In 
fact, there are a number of things in this 
photograph that will interest the student- 

Spherical Aberration. An examination 
into the effect of spherical aberration points 
to the fact that it operates mainly to cause 
impurity of the light, by reason of the fact 
that those rays which draw in toward the 
center earliest must naturally reach somewhat into the center 
of the spot, and coming, as they do, from the outer edge of 
the lens, they carry with them considerable color. 



This, so far as I am able to determine, is the principal 
practical effect of spherical aberration. It amounts to a dis- 
coloration of the light, and hence a diminution of its brilliancy, 
though it may or may not be sufficient to be perceptible to 
the eye in individual cases. 

Also spherical aberration, if excessive, will cause the spot 
at the aperture to consist of a series of circles of light in- 
stead of an evenly illuminated field, and as this plane is 
refocused at the screen, there will, if there is an absence of 
rays at the center, be a dark spot or "ghost," or if more of 
the rays are reaching the center of the spot than its edges, 
high lights will result. This is usually the result of the film 
cutting the beam of light too far from the actual mean focus 
of the crater, but there are, nevertheless, other conditions 
which result in high lights and shadows on the screen, and 
spherical aberration may result only in uneven illumination. 
There is practically no bad effect from spherical aberration 
through the stereopticon because the rays reach the slide 
before they are displaced, but chromatic aberration will show 
if the rays from the outer edges/ of the condenser pass 
through the slide. 

Chromatic Aberration of the Condenser Beam. In Plate 11, 
a crater is constructed by cutting an aperture in a piece of 
cardboard and placing a | ^CARDBOARD 

piece of ground glass K I/MNHOU- 

behind it. Back of this 
is placed a 100 C. P. 
incandescent lamp. The nLAMENT 
crater and screen are 
placed at conjugate foci 
of the condensers. The 
screen corresponds to 
the aperture plate of the Plate 11, Figure 52. 

machine. A piece of cardboard pierced with a pinhole is 
placed as shown in Plate 11. 

The results as observed upon the screen, Plate 11, are: the 
crater is focused in full definition on the screen, but it is 
colored with the shades of the spectrum in the manner shown. 
Now it has been demonstrated by the Kinemacolor process 
that all the colors of the spectrum can be reduced to ap- 
proximately two shades, viz: a reddish-orange and blueish- 
green, which for the sake of clearness we will call orange 
and green. 

In Plate 11 A are shown the same conditions described in 
connection with Fig. 1, except that the colors of the spectrum 



have been reduced to the two primary shades, viz: orange 
and green. Notice that at the screen (or aperture) the 
colored rays combine and form white light. 

Now, if the process shown in Plate 11A be continued, and 
a very large number of rays be drawn, using orange and 
green ink, the result will appear as shown in Plate 11B, in 
which it is observed that the beam is inclosed by an orange 
envelope, Which is thickest toward the central part of the 
beam and comes to a 
point or disappears en- 
tirely at the aperture 
and the condenser. The ^ 
beam has a core in the 
center which is com- 
posed ofi the violet, :,.../?&xr v j, N ncys. 
blue, and green shades 
of the spectrum. The 
white part of the beam 
is caused by the mixture of the two other primary shades, but 
the mixture is not perfect at all positions. At the section AA, 
Plate 11B, the white light is most pure, but as it approaches the 
position of section BB, the colors at the violet end of the spec- 
trum commence to predominate, so that at section BB, the white 
zone has changed to a dirty purple. In< view of this condition it 
is not difficult to understand why a ghost appears in the 
screen when the aperture is brought back too far toward 
point BB. When properly located all the colors of the beam 
finally combine at the .aperture to form pure white light, and 
since it passes from .aperture to objective, all light beyond 
the aperture is pure white. It is also noted that the light at 
section AA, Plate 11B, is pure white. 

Plate 11A, Figure 53. 

Plate 11B, Figure 54. 

Now it must be remembered that the results shown in 
Plate 11B can only be approximately true, since all the colors 
of the spectrum, which are infinite in number, have been 
reduced to only two shades. Even if only seven colors had 
been used in the drawing, the straight lines in Plate 11B 


would show as curves, and more closely 
resemble the true shape of the actual 
beam. Nevertheless, when a small screen 
is placed at different sections of the actual 
beam, the results show a very close agree- 
ment with the theories set forth. 

In photographing the beam, only the 
white and green zones are actinic and 
show in the photograph, and by observing 
Plate 11B, it is seen that the theoretical 
shape of the combined white and green 
zones agrees very closely with the photo- 
graph. But even to the eye the beam has 
a curved shape, which is probably due to 
the existence of infra red at the outer 
edge of the orange envelope. 

It is finally seen, as a further point in 
practical application, that one of the im- 
portant functions of having the crater in true 
focus at the aperture is to purify the light 
and avoid color effects. The aperture may 
be placed a little forward of the focal plane, 
|^ but should never be behind it. 

Some of the practical effects of chro- 
matic aberration are seen in Plate 11C. It 
will be observed that whereas the holes in 
the metal shield covering the condenser 
are of equal size the lower ray is much 
the stronger. This is partly due to its 
position, but also to a very considerable 
extent to color in the upper ray which 
reduces its actinic effect on the photo- 
graphic plate. 

Another important point in connection 
with the condenser/is loss of light through 
poorly polished, unevenly finished surfaces, 
and through discoloration/ of the glass. 
Of late there have been those who have 
advocated the addition of yellow to the 
condenser lens glass, with the idea of mel- 
lowing light. With this I cannot agree. 
I think it is hardly necessary to enter into 
a discussion of the matter, and most emphatically advise 
operators to avoid the use of lenses containing discoloration 
of any kind. In selecting a condenser lens first examine its 



surface, and, unless it presents a perfectly smooth, polished 
appearance, and evidence of having been ground to the true 
surface, reject the lens. In order to perform its function 
properly a lens must be a perfect segment of the surface of a 
sphere, and this perfect shape can only be obtained by grinding. 




Plate 12, Figure 56. 

It cannot, by any stretch of imagination, be had by merely 
polishing the surface of a molded lens. 

Stop .and consider the matter for a moment. In order 
to secure even approximately perfect results in illumination 
at the spot it is necessary that all light rays emanating 


from any point on the crater and falling upon any point on 
the surface of the lens be so refracted that they will reach 
the same point in or on the spot. 

Now this can only be accomplished by a perfectly true lens 
surface, and it therefore follows that if the surface of the 
lens be not perfectly true, some of the rays are going to 
be refracted properly and some are not, and this of necessity 
means loss in effectiveness. With this in view I would call 
the attention of theatre managers to the fact that the cheap, 
molded condenser lenses, having an uneven, wavy surface, 
may be cheap in first cost, but are a mighty expensive article 
in the long run, because of the fact that, since it takes current 
to produce light, and you have to buy the current, anything 
which makes for ineffectiveness in illumination means a 
waste of current, hence you are simply saving a small sum 
of money in the original cost when you buy a cheap condenser 
lens, and are paying out money every minute you run for 
current to produce light which the cheap lens is wasting. 

Also reject any lens which does not measure exactly 4^2 inches 
in diameter and which has an excessively thick edge. Con- 
denser lenses should be exactly 4J^ inches in diameter, and 
should come down to an edge but little if any thicker than 
one-sixteenth of an inch. A thick edge means unnecessary 
glass; therefore unnecessary absorption of light. In Plate 12 
A shows the wrong and B the right lens edge. It is im- 
portant that the edges of condenser lenses be of standard 
thickness, .and that their diameters be exactly 4H inches, 
because not only is excessive glass wasteful (it is impossible 
for manufacturing reasons to bring the edge right down 
to a thin edge at a 4^2 inch diameter) but with edges of 
varying thickness it is impossible to make the lenses fit 
properly in many of the machine lens holders; also any 
change in diameter alters the fit of the lens in the holder, 
and these variations will render it practically impossible for 
the operator to properly line up his lens system. I would sug- 
gest that operators pay careful attention to this matter be- 
cause lens manufacturers seem to think that "near or about" 
is good enough, both in diameters and lens edge thickness. 
They will only change that attitude and come down to a 
fixed standard when a large number -of kicks are registered 
by purchasers. I have pointed out the reasons why diameters 
and lens edge thickness should be absolutely standard. I 
think you will have no trouble in recognizing the fact that 
these reasons are sound. It is now up to you to compel 
lens manufacturers to produce a standard article, and I 


suggest that you insist on an exact 4 l / 2 inch diameter and a 
lens edge thickness exactly one-sixteenth of an inch. It 
is quite true that to thus standardize lenses might add 
somewhat to their cost, but even so, it will be money saved 
in the end, no matter from what angle the proposition be 

In selecting your condensing lens, first examine its surface, 
and if it is not perfectly smooth and highly polished it is not 
a good lens. Next look through the lens edgewise, and if it does 
not show clear (has any trace of color when looked through 
that way) reject it. It is not a good lens. 

If you have any doubt whatever as to the inadvisability of 
using lenses containing color, either purple, greenish or yel- 
low, break a clear white condensing lens in half; also break 
a lens containing discoloration in half, put these two halves 
in as the front lens of your condenser combination, being 
certain the rear lens contains no color, and project the clear 
light on the screen through the stereopticon lens. I think the 
appearance of the screen will satisfy you thoroughly as to the 
advisability of rejecting any lenses containing any color what- 
ever. This experiment should only be tried through the stereo 
lens, with which the two halves can be focused at the screen. 

In a camera the lens receives rays directly from an object 
and delivers them directly to the screen (plate). 

In the projector there are two absolutely separate lens 
systems, one of which receives its rays from the other, and 
one of our problems is to so join these two systems that the 
film picture will not only receive a maximum of illumination, 
but also that that illumination shall be evenly distributed over 
the entire area of the photograph, and that the second or 
objective system be enabled to pick up the light rays delivered 
to it by the first or condenser system, with the least possible 
amount of loss. 

Now these various propositions look reasonably simple, but 
there are, in fact, some very intricate problems involved. 
With relation to the condenser system, there is one point 
on which we have very little accurate data, viz.: the exact 
diameter of the crater for a given amperage. Until this 
matter is accurately determined our efforts in that direction 
can only be approximately correct, and possibly there may 
always be some differences in this item since doubtless differ- 
ent carbons will slightly alter crater size for a given am- 

One exceedingly important point, which must be borne care- 
fully in mind, is that when the source of illumination is greater 


than a point the light ray from the condenser can never be 
brought to a point, for example : Assuming the crater to be 
an object, and the spot on the aperture an image (which is 
the exact condition), if the crater be 4 inches from the apex 
of the curved surface of the back condenser, and the spot on 
the aperture 16 inches from the apex of the curved surface 
of the front condenser, then the diameter of the spot on the 
aperture will be four times the diameter of the crater, of 
which the spot is an image, and the spot will be the nar- 
rowest part of the condenser beam, since at this point the 
beam will begin to diverge, therefore we cannot consider the 
condenser beam as coming to a point further on, as it has 
always been supposed to do. 

Not only have we discovered the fact that there is a direct 
ratio between the diameter of the crater and the diameter of 
the spot on the cooling plate, but we have also found that in 
order to obtain the most even illumination of the entire aper- 
ture it is necessary that the crater be "in focus" at the aperture 
of the machine, or in other words, that the crater and spot be at 
the respective points of conjugate foci of the condenser lens. 

Now in order to understand this some of you must do a 
little studying. Take a condenser lens and hold it near the 
wall of a room, opposite an open window, and you will find 
that with the lens at a certain distance from the wall you 
get a fairly good image or picture of the scene out of doors 
on the wall. This means that the lens is at a distance from 
the wall equal to its focal length, or, in other words, in a posi- 
tion where rays emanating from a point on an object are 
brought to a focus in the image, not where the light beam, 
as a whole, is brought to a point, which it never is. Move 
the lens further from the wall and the ray increases in size 
and is quickly lost. 

Some may dispute this, and cite the burning glass in proof. 
Well, the point to which the burning glass apparently brings 
the rays is not a point at all, but merely an exceedingly small 
image of the sun. 

Now, taking the condenser as a whole, the crater of the 
carbon takes the place of the scene out of doors, and the 
aperture of the machine the place of the wall. Of course 
the image is formed much further away than was the case 
with the lens held near the wall, but this is by reason of 
the fact that the crater (object) is close to the lens, whereas 
the out-of-door scene was far away. If a single lens were 
used, instead of a double one, these distances would again 
be altered. 


And now the question comes: When is the crater in focus 
at the aperture? This is a somewhat complicated proposition, 
in which we must take into consideration the known fact 
that spherical aberration exists in the condenser system, 
and the further fact that the crater does not set parallel to 
either the condensing lens or the film; therefore, due to the 
latter equation, there is bound to be precisely the same effect 
at the spot as there is when the machine sets at an angle 
to the screen. In other words, since the surface of the crater 
is not parallel to the lens the whole crater cannot possibly 
be put in sharp focus at the aperture, or anywhere else. We 
must therefore adopt a "mean focus point" or point of actual 
mean focus, since we cannot expect to get a sharp focus of 
the entire crater for reasons already pointed out. The point 
of actual focus must, due to spherical aberration, be beyond 
the plane where the rays from the outer edges of the spot 
would naturally focus, they being focused nearer the lens 
than the rays forming the center of the spot; therefore the 
plane of actual mean focus will to some extent have the 
appearance of back focus at the cooling plate. In fact, the focus 
of the crater may be assumed to occupy any position between 
the circle of least confusion, which may be recognized as a 
round spot with reasonably sharply denned edges, and a 
plane a few inches in front of the circle of least confusion, 
which latter may be recognized as a white spot surrounded 
by a bright blue outline. This blue spot consists of the 
aberrated rays on the back focus, the white spot in the 
center of the haze being the image of the crater. 

The ordinary practice of the operator is to carry a sharp, 
round spot at the cooling plate, rather than the actual focus 
of the crater, and so long as he can maintain this spot small 
enough, and still keep 'his arc near enough to the back con- 
denser to give good illumination, all is well provided he can 
also maintain a distance sufficiently great between the con- 
denser and aperture to prevent the rays in front of the 
aperture from diverging beyond the limits of the objective 
lens. See Plate 8. 

When the distance between the condensers and film be- 
comes too great to maintain a suitable size focused spot at 
the aperture and still keep the arc near enough to the con- 
denser, the only alternative is to focus the actual image 
of the crater, which is surrounded by a blue haze, at the 
aperture, and in order to do this it is necessary to utilize 
the whole length of the machine table, and also the shortest 
focal length condensers usually carried in stock, viz: two 



6H inch, in order that the white center be sufficiently magni- 
fied to fully cover the aperture. The spot produced by this 
arrangement will not look very picturesque on the cooling 
plate, but will give very superior results on the screen. If the 
amperage be very heavy it may be necessary to use one 
6 l /2 and one 7 l /2 condenser, or if very light then one 5^ and 
one 6 l /2 will be best. In this we assume the limit of the 
machine table to be such that approximately twenty-two 
inches can be had between the condensers and aperture. 

Note. You cannot have too great a distance between the 
condensers and aperture, provided you keep your arc near 
enough to the back condenser. 

The tables given in this article merely provide the mini- 
mum, and the condensers therein named are for working 
w^;h the spot at the plane of least confusion only. I would 
suggest that any condition calling for greater focal length 

condensers than 6^2 and 
iy-2 will be better taken 
care of by using the 
spot with the blue haze 
and shorter condensers 
and the limit of dis- 
tance between the con- 
denser and film. 

Remember this: The 
spot itself is actually an 
image or picture of the 
crater. It therefore fol- 
lows that any attempt to 
use both craters with 
A. C. will set up diffi- 
culty, since it will, in 
the very nature of 

things, be extremely difficult, if not impossible, to get their 
images properly superimposed upon each other. 

Some operators have got splendid results from meniscus- 
bi-convex condensers, whereas others have reported no per- 
ceptible advantage in their use. It is all a matter of local 
conditions. Operators who have difficulty in getting their 
arc near enough to the condenser are the ones who will get 
best results with the meniscus-convex combination, by reason 
of the fact that they gain at least Y^ of an inch between the 
arc and the condenser, owing to the fact that the planes from 
which the conjugate foci are measured are changed that is 
to say, they are not the same with the meniscus-bi-convex as 

Plate 13, Figure 57. 



they are with two plano-convex (see Plate 13). This 
is owing to the introduction of two more curved surfaces. 
The result is less enlarge- 
ment of the crater. On the 
other hand, the operator who 
can get near the condenser 
with his arc and still have a 
small spot will find but little 
benefit in the use of the 
meniscus-bi-convex set, pro- 
vided the meniscus-bi-convex 
and plano-convex lenses be 
of the same quality, except in 
reduction of spherical aber- 

The theory upon which the 
action of light rays through 
the projector system, as set 
forth in this article, is based, 
is a difficult matter to ex- 
plain in such way that the 
reader or student will grasp 
the idea. Light action is one 
of the most difficult things 
imaginable to describe intel- 
ligently by reason of the fact 
that in drawing diagrams 
representing light action one 
is limited to the examination 
of the action of one, two or 
possibly a dozen rays out of 
literally millions and, as a 
general rule, the student has 
difficulty in considering the 
single ray or the few rays 
shown in the diagram as 
being representative of the 
action of countless numbers 
of rays which accompany it 
but are not shown. 
' In this connection, as a di- 
gression, it might be interesting 
to know that scientists tell 
us that a bundle of thirty-six Plate 14, Figure 58. 


light rays will have approximately the same area as that 
of a single human hair. 

Beginning with a fact with which all are more or less 
familiar, viz.: that from each point in a light source rays 
radiate in all directions (in the case of a projection arc light 
crater it would not be literally in "all directions," but in all 
directions over an area covering what would be practically 
equal to one-half the surface of a globe) until they meet 
with some obstruction. After leaving the crater the first 
obstruction encountered is the condensing lens through which 
the rays must pass. This gives us countless numbers of 
cones of light as A-l-2, B-l-2, C-l-2, Plate 14, each cone 
having its apex at a point in the crater, and its base on the 
surface of the condensing lens. The sum of these cones 
represents the total light passing through the condenser. 
Each one of these cones is made up of diverging rays ex- 
clusively, up to the rear surface of the condensing lens. 
With; this I believe we all will agree, and thus endeth the 
first part. 

But when we come to examine into their action beyond 
the rear surface of the condensing lens we find that the fore- 
going does not fully elucidate or make clear the entire prob- 

First: From each point on the crater we have rays enter- 
ing every minute pinpoint on the surface of the condenser, 
therefore through each point of the condenser we have pass- 
ing a cone of converging rays, each cone carrying a complete 
image of the crater, as per A-C-2, A-C-1, so that we are also 
entirely correct when we consider the total light passing 
from the crater through the condenser as consisting of 
countless numbers of cones of converging rays having their 
apex at a point on the condenser at 1-2, Plate 14. It will 
thus be seen that while we do not actually have two sets of 
rays we do have a double light action. It may very reason- 
ably be asked: "If the first part includes the total rays pass- 
ing from the crater through the condenser, and the second 
part merely does the same thing in a different way, why 
bother with the second part at! all when the action first 
described is more generally understood?" 

The reason for analyzing the action of light rays complete- 
ly and describing the second part is because it gives us a 
clearer understanding of what follows. 

Now having in mind one of the cones A-C-1, or A-C-2, 
Plate 14, it will be readily seen that rays A-l and C-l meet- 
ing at a point on the condenser will, even though refracted, 



cross at the plane of the condenser. This can easily be 
proven by using a refractometer. It therefore follows that 
as the total rays entering and passing through the condenser 
from the crater may be considered as consisting of count- 
less cones having their apex at a point on the condenser, the 
crossing point or reversal of the image must, in the very 
nature of things, take place at the rear plane of the rear 
condenser and at no other place. Undoubtedly the rays do 
cross each other before reaching the condenser plane, but only 
when on their way to and from a point which is receiving a 
complete image of the crater. 

This action is perhaps made most clearly intelligible, and 
may be best adapted to use in this article by considering 
cone A-l-2, cone B-l-2, cone C-l-2, cone A-B-1, A-B-2 and 
B-C-2 (remembering that these are but representative of 

Plate 15, Figure 59. 

millions of other similar cones at other pinpoints on the 
crater and condenser) as being two sets of rays. Please 
understand that we do not mean by this that there actually 
are two sets of rays, but merely use that term as a con- 
venient medium through which to describe certain action of 
the light which really is the same group of rays acting in two 
different ways. 

Theory of double action may perhaps be made more un- 
derstandable by means of diagram, Plate 15, which is a 
diagrammatic representation of pinhole photography. 

In Plate 15, at A, we see a diagrammatic representation of 
pinhole photography, in which rays by the millions go in 
every direction from every point of arrow B-C, but only those 


rays striking pinhole D can pass through and form an image 
on the screen at E-F. That is the idea we had in mind in 
saying that one set of rays projected the whole crater. To get 
the point of view, you must consider each minute point on the 
back plane of the condenser as being a pinhole, and as a matter 
of fact it does act in exactly that way, therefore each minute 
pinhole point of the condenser will receive one ray from each 
pinpoint of the crater and will therefore project an image of 
the crater, as a whole, to the aperture of the machine. This 
same thing is shown photographically in Plate 16, in which 

Plate 16, Figure 60. 

A is the machine aperture, covered by a plate in which are 
two pinholes, and B the back factor of an objective, covered 
with a plate containing one pinhole. The action is that rays 
from the lower half of upper cone X pass through as ray Y, 
whereas from the upper half of cone X pass through as ray 
Y. The photo is a poor one, as it is extremely difficult to 
get a good picture of such weak rays. A comparison will 
reveal the fact that the action in A, Plate 15 and in Plate 16, 
is identical. 

The second set of rays, viz.: those emanating from a point 
on the crater, represented by cones A 1-2, and B 1-2, and C 
1-2, Plate 14, project to the same aperture, in converging 
lines, rays from every infinitesimal portion of the crater, and 
that is the real explanation. 

The foregoing theory is not altogether coincided in by 
some, but the fact, nevertheless, remains that it is the only 
one by means of which we can explain one phenomenon, viz.: 
why the beam of light is round as it emerges from the objec- 
tive, and continues so for a distance varying with the focal 
length of the lens, and thence to the screen is rectangular. 
And now comes the difficult part to explain. 

In Plate 14 we see a diagrammatic representation of Grif- 
fiths' theory, as applied to the condenser system. In Plate 16 
we see, in photography, precisely the same thing as applied to 



the objective lens. Always bear in mind 
one fact, viz.: the optical action of the 
objective lens and the optical action of 
the condensing lens is in every respect 

Now to follow this matter through 
we will consider Plate 17, which is a 
photographic representation of light 
ray action in an objective lens, in 
which X is a shield containing a 
standard machine aperture, covered by a 
brass plate containing two pinholes. Y 
is a standard projection lens, with one- 
half of its barrel cut away, 1 and 2 be- 
ing respectively the back and front 
factors of the lens, though 2 is hidden 
behind its container. This photograph is 
made with the aperture and the lens 
in actually working position, and with 
the light projected through the con- 
denser in the ordinary way, under 
actual operating conditions. You will 
observe that the light coming through 
the upper pinhole, Plate 17, diverges 
into a cone, which corresponds to 
cone A, 1-2, Plate 14. This cone cov- 
ers very nearly the full aperture of the 
lens. The light passing through the 
lower pinhole does exactly the same 
thing, and the two cones begin to in- 
termingle at L, and from there on to 
the lens a small central light pyramid 
is shown, the upper half of which is 
the upper edge of the lower pinhole 
cone, and its lower edge the lower 
edge of the upper pinhole cone. Be- 
yond the back factor of the lens, be- 
tween the two lens factors, you can 
easily trace the action. And it is made 
clear in this photograph that the bend 
which starts the final crossing or trans- 
position of the rays takes place at the 

first or back surface of the first or back combination of the 
objective, even as it takes place at the back surface of the rear 
lens, Plate 14. The action, as between the diagram, Plate 


i; y <i--uii : ;- < ' *,:: * ;!W ' 

14, and the photograph, Plate 17, is precisely identical in 
every way. As the light leaves the front end of the objective 
you will observe that rays of the two are not entirely inter- 
mingled but that the mingling can be traced clear through 
by the brighter light. This intermingling condition continues 
out to where the cone projected by the upper pinhole 
has passed down sufficiently to entirely leave the cone 
thrown from the lower pinhole, which latter is at the same 
time passing on its way to the screen. The action of these 
two cones of rays are typical of those passing through every pin- 
point of the film picture. 

Each individual point of the film acts as does the pin hole, and 
dn sending a cone of rays forward exactly like those shown at L, 
Plate 17, and, since each of the rays contained in each of these 
cones carries an image of the point of the film through which 
it passed, it follows that all these rays must be refocused at 
the screen; it also follows that the actual crossing is as 
shown in the photograph. I believe this photograph will be of 
vast interest to operators. 

And now let us apply the theory of the "two sets of rays," 
and see how it works in practice. Operators have long been 
puzzled as to why the spot on the revolving shutter is round 
when the shutter is close to the lens, whereas a little further 
ahead, toward the screen, it becomes rectangular. The 
two-ray idea is the only theory that seems to account for 
this, and it is to some extent this fact which has convinced 
me of its absolutely correctness. 

First fix the following firmly in your mind. There are two 
complete but entirely separate optical systems in the projec- 
tion machine lens system, which are, in effect, combined into 
one. Remember that the optical action of the condenser and 
objective is precisely the same. In fact the condenser is a crude, 
extremely imperfect objective lens ; therefore, we have in effect 
two objective lenses joined together, and the object ds to so 
join these two systems together that there will be a maximum 
of illumination of the object to be projected, and the rays 
directed against and through this object by the first system 
must be so joined to the second system that there will be a 
minimum loss of light, and no opposition created by the 
refractive power of one system as against the refractive 
power of the other system. The second system (the objec- 
tive) picks up the rays delivered at the aperture by the first 
system (the condenser) exactly as they are delivered by it, 
therefore when the distance of the crater from the rear con- 
densing lens is so proportioned with relation to the distance 


from the back plane of the rear condensing lens to the aper- 
ture that the image of the light source (the crater) is in 
exact focus at the aperture, and the spot is of such size that 
the circle of clear, white light covers the aperture completely, 
with sufficient margin to enable the operator to maintain a 
clear field, then the plane of light at the aperture, where the 
objective picks up its rays, contains the maximum illumina- 
tion, and, moreover, that illumination is evenly distributed 
over the entire area of the aperture. 

And now let us see how Griffiths' two-sets-of-rays theory 
squares up with what is actually observed to take place in 
practice. It has always been somewhat of a puzzle to operators 
why the rays emerging from the objective lens do not immediately 
diverge straight to the screen, instead of converging a little and 
then diverging (this is only noticeable when the condenser image 
is smaller than the aperture of the lens), and also that they 
have a more or less round form until they reach the narrow 
part of the beam, from which plane the shape becomes rec- 
tangular. For the sake of convenience we will refer to that set 
of rays coming from a point of the crater as the crater set, 
and those coming from the whole -of the crater to a point of 
the condenser as the condenser set. 

The first point to determine is, in what manner do these two 
sets of rays reach the objective lens, after which we may 
compare the result that should occur with these two sets of 
rays with what we actually observe in practice. It has already 
been said that the condensers act precisely as would a crude 
objective lens, therefore, the crater set, being the diverging set 
of rays emanating from a point of the crater, must meet again 
at a point of the crater image (spot of the aperture), and as 
the film is at this plane, these rays pass through a point of the 
film cross and again diverge to the objective lens. Thus our 
crater set reaches the objective from a point of the film, and 
their shape will correspond to the shape of the aperture of the 
condenser. If a slide carrier is used the ray will, in the very 
nature of things, be rectangular, but if the condenser opening 
be unobstructed the ray will, of course, be round. 

Now, let us trace the condenser set from the crater to the 
objective lens. It has already been explained that each 
point of the condenser is receiving a ray from every point of 
the crater, so that through each point of the condenser a com- 
plete image of the crater is being projected, and as these rays 
diverge from that point to every part of the crater image 
which they carry, they must carry a full film image to the 
objective lens, arriving at the same as a rectangle somewhat 


larger than the aperture, therefore, the "condenser set" of 
rays arrive at the objective carrying a full film image. It 
therefore follows that if a slide carrier be used, both sets of 
rays will arrive at the objective lens with an over-all rectang- 
ular outline, one, the crater set, having the shape of the slide 
carrier, and the other, the condenser set, having the shape of 
the film aperture, the condenser set carrying a full film image, 
and the crater set carrying the image of a point of the film. 
Now these two sets of rays, one emanating, so far as concerns 
the objective, from a point of the film and the other from a 
point of the condenser, have a different angle of divergence, 
and must therefore be brought to a focus at two different planes. 
Those coming from a point of the film, and, incidentally, form- 
ing the crater image, must focus at the film image, viz: at the 
screen, and those coming from a point of the condenser must 
focus at the point of the condenser image, and as the angle 
of divergence of the condenser set of rays is much narrower 
than the angle of the divergence of the crater set, it follows 
that these rays will meet (focus) much nearer the lens than the 
other set. In fact their focusing point will be identical with 
the position of a photographic plate in a camera when taking 
a picture of an object as far away from the camera lens as 
the condenser is from the objective, the camera having a lens 
similar to the objective. And this is exactly where we do find 
the condenser image, viz: a little further in front of the objec- 
tive lens than the back focus at which it is working. The 
existence of the condenser image at this position proves that 
the condenser set of rays, the existence of which has met with 
so much opposition, is really the key to the whole problem, be- 
cause the condenser set of rays carry the full image of the 
film, and as they come from a point of the condenser the film 
image is reversed at the condenser image. 

But, I hear some one ask, if both sets arrive at the objec- 
tive rectangular in form when the slide carrier is used, why 
do they emerge from the objective round in form? . A bundle 
of rays from a point of the center of the condenser will arrive 
at the objective lens as a rectangular a little larger than the 
aperture, its style varying with the B. F. of the lens, but a 
bundle from a point near the edge of the condenser will arrive 
at the lens in a different location, so that only a part of the 
image from this point enters the objective. The sum total of 
all the rectangles from every point of the condenser is a 
rectangle much larger than the aperture of the lens, the result is 
that the beam, as a whole, is trimmed into a round shape. But, 
you may ask, if the rectangle has its corner rounded off, why 


does it show rectangular again after passing the condenser 
image? You will observe that the rectangle from one point of 
the condenser is smaller than the rectangle representing the 
whole beam of light, so that only one corner is clipped off 
by the lens, and while this corner is on the outside up to the 
condenser image, thereafter it is on the inside, and as there 
is a pyramid from each point of the condenser image, the 
defective corner is hidden by other pyramids from more cen- 
tral portions of the condensers which are projecting perfect 

This trimming process is also applied to the crater set of rays, 
whether they are from a rectangular slide carrier or a round 
condenser. No matter what shape they are, each ray passes 
through the condenser image at a point corresponding to that 
through which it passed through the condenser; therefore the 
two sets of rays emerge from the lens converging, the crater 
set carrying an image of a point of the film meeting at a point 
of the film image at the screen, while the condenser set meets 
at a point of the condenser image, and then diverge to the 
full screen. This is why you can almost completely cut the 
beam of light at the condenser image with the shutter, and 
still have a full image of the aperture at the screen. So that it 
will be seen that that much mooted question which has been 
cussed and discussed for lo these many years: "Where do the 
light rays cross?" is answered by saying that they are crossed 
at the image of the condenser when projecting moving pictures, 
and in the center of the lens when the stereo lens is used, and 
therefore the old theory holding that the light rays crossed 
in the center of the lens still is true when speaking of lantern 
slide projection. The next question is, if the film image is 
crossed and reversed at the condenser image : why is the stereo 
slide image not crossed there ? The answer is : The film 
photograph is being projected from the crater image plane, 
whereas the stereo slide photograph is being projected from the 
condenser plane, with the result that the rays from one point of 
the source carry a full slide image which crosses where the rays 
meet, viz: the image of the source, or crater, and as the center 
of the stereo lens is the best location for this plane, it is quite 
true that the rays cross in the center of the lens when projecting 
stereo slides. 

Matching the Lenses. The following tables have been 
worked out as a final result of the foregoing theories. By 
their use the operator will be enabled to match up his lens 
system accurately and with as great precision as the limita- 
tions of present day apparatus will allow. 



g_ e jo 

/e 17 

VST /.a 




.3 '4 




S/O 2./S 





-2/ZZZ22fK t 











U?6 43d W3 4S2 

&fc 442. ?>? 476 




4.1 / 4J1 

^J Z'/e26ft 















1/7? UK 3^ VZ5 4 $76 tote tttt fW MM 64- 






74- TfZJ *'(' Ztf X7J 


Table 1, Figure 62. 

Decimal Equivalent. 1/16 = .0625 ; 1/8 = .125; 3/16 = .1875; 
1/4 = .25; 5/16 = .3125; 3/8 = .375; 7/16 = .4375; 1/2 = .5; 
9/16 = .5625; 5/8 = .625; 11/16 = .6875; 3/4 = .75; 13/16 == .8125; 
7/8 = .875; 15/16 = .9375. 


Table 1 is what might be termed the "angle table." It 
represents the tabulated results of what is shown in the 
diagram in Fig. 4. In order to apply this table proceed as 

First measure the diameter of the opening of the objective 
lens. Next, with the picture in exact focus on the screen, 
stick a rule through the aperture of the machine and place 
it against the back surface of the back combination of the 
objective lens, and measure the exact distance from the lens 
to the film, or, in other words, from the lens to the surface 
of the film track on the aperture. This will give you the 
exact back focus of the lens at the position in which it works. 
This is of the greatest importance because any given lens 
may work in different positions under different circumstances. 
Having found the measurement of the diameter of your ob- 
jective, and its back focus when in working position, proceed 
as follows : 

In the extreme right-hand column find the number most nearly cor- 
responding 1 to the back focus at which your lens is working. Opposite 
this number, in the extreme left-hand column you will find the smallest 
lens diameter permissible at that back focus, and at the top of the 
right-hand column we see that the condensers must be two "7%s," with 
22 inches between the apex of the front lens and the film. For ex- 
ample: Suppose the B. P. to be 4% and the-* lens diameter 1% inches. 
At the sixteenth line down we find 4.52 (practically 4%) in the right- 
hand column, and opposite, in the left-hand column, 1%. We therefore 
see that 1% is the least permissible lens diameter, and that our lens 
is unsuitable to the work in hand. Looking at the top of the right- 
hand ^column we see that with the 1%-inch lens we must have two 7% 
condensing lenses with not less than 22 inches between the apex of the 
front lens and the film. This is the extreme condition. Looking in 
the third column from the right, however, one line further down we 
again find 4.52 and discover that with a lens 1 15/16 inches in diam- 
eter we may use two inches less between condenser and film, though 
two 7% lenses are still required. Again looking, we find 4.60 in the 
fourth, 4.6 in the fifth and so on over to the twelfth column, where we 
find 4.540 In the bottom row and see that with a lens 3 inches in 
diameter we could use one 5% and one 6% condenser, with 11 inches 
from apex of front lens to film the extreme condition in the other 

Table 2 shows relative distances of conjugate foci and 
amount of enlargement of the image of the object, the object 
being the crater or source of light and the image the spot on 
the aperture. 

Diagram A, Plate 13, shows the points from which the dis- 
tances are measured with piano convex combinations. 

Diagram B, Plate 13, shows the points from which the dis- 
tances are measured with a meniscus-bi-convex combination. 
With the piano convex combination X equals the distance 
from the crater 'to the curved surface of the back condenser, 



and Y equals the distance from the curved surface of the 
front condenser to the aperture. 

With the meniscus-bi-convex combination X equals the dis- 
tance from the crater to a point l /% of an inch in front of the 
convex face of the back condenser, and Y is equal to the 
distance from the center of the bi-convex condenser to the 

The essential difference between the meniscus-bi-convex and 
the piano convex is that there is less enlargement of the spot 
on the aperture with the former when the E F is the same 
in both cases. 

The enlargement with both sets is equal to distance Y 
divided by distance X, both in inches. 

When meniscus-bi-convex condensers are substituted for 
piano convex we increase X by J^ of an inch and decrease 
Y by the thickness of a piano lens, because the center of the 
bi-convex occupies the same position as the plane of the 
piano convex. 

Example. Piano convex R = 4, Y = 16, therefore enlarge- 
ment equals 16 -f- 4 = 4 times, so that the spot will be 4 times 
the diameter of the crater. Meniscus-bi-convex X = 4%$ and 
Y = 15, therefore the enlargement equals 15 -f- 4^ = 3.83 

The necessary enlargement of the crater will depend on the 
number of amperes we use, so, knowing the distance Y, which 

is the distance the ob- 

*HSI. <=? & 





650 4-87 1-33 



















Table 2, Figure 63. 

jective calls for between 
the condenser and the 
aperture, see table 1, 
we look for that dis- 
tance under the en- 
largement head we re- 
quire, but we must 
choose it in conjunc- 
tion with X, remember- 
ing that X is the dis- 
tance between the crater 
and the condenser, plus 

thickness of the lens, and that with the meniscus-bi-convex 
the enlargement will be less than what the table calls for, 
we see the figures we need will be those giving slightly a 
greater enlargement. If with piano convex we need a four 
time enlargement, with meniscus-bi-convex we could choose 
about a 4j time enlargement. An examination of the tables 


will make this clear, and will show the advantage of using 
the meniscus-bi-convex set where it is difficult to obtain a 
spot small enough and still keep the arc at proper distance 
from the lens. 

Another important point which has been determined is that 
in thousands of instances objective lenses now in use are 
not large enough in diameter. 

With reference to the difficulties that may be encountered 
with the large aperture lens and the revolving shutter the 
following facts will be of interest: 

The diameter of the beam of light at its narrowest part 
in front of the objective is in proportion to the distances 
between the condenser and aperture and the equivalent focus 
of the objective lens. That while it is the equivalent focus of 
the objective lens that determines where the crossing point 
of the rays in front of the objective will be, changing the 
distance between condensers and aperture changes the diam- 
eter of the narrowest parti of the beam considerably and 
also causes a small change in the position of the narrowest 
part, which is the image of the condenser aperture. In- 
creasing the distance between the condensers and aperture 
decreases the thickness of the beam at its narrowest part, 
and vice versa. So that increasing the diameter of the ob- 
jective lens, and at the same time shortening the distance 
between condensers and aperture, operates to increase the 
diameter of the beam at its narrowest point; but if we in- 
crease the diameter of the objective lens without altering 
other conditions, the width of the beam at its narrowest point 
does not increase. 

The crossing point of the light beam will hardly be discern- 
ible when the distance between condenser and aperture is 
short, owing to the fact that the image of the condenser aper- 
ture is further from the -lens, and consequently larger, so that 
rays to this image do not have to converge, therefore the whole 
beam of light will appear to diverge from the lens. 

In this connection it is interesting to note that increasing 
the distance between condensers and aperture may be used 
to eliminate travel ghost when the shutter blade is too nar- 
row. The effect of withdrawing the lamphouse from the 
machine head has the same effect on the narrowest part of 
the beam of light as withdrawing the arc from the condenser 
has on the spot at the aperture. 

In conclusion: Until such times as objective lenses and con- 
densers are brought up to our requirements the following 
points should be observed: Always have the crater as near 


as possible to the condensers say between 3^ and 2*/z 
inches, according to the amperage used, and always have the 
greatest possible distance between the condensers and aper- 

These two conditions in some cases conflict with present ap- 
paratus, therefore, it may be necessary to compromise between 
the two. But the compromise means loss in efficiency. 

For convenience in the use of these tables the decimal 
equivalents for fractions are given. I believe the foregoing is 
reasonably clear at least sufficiently so that the table can be 
readily applied by the operator. 

Caution. In measuring the back focus of your lens be very 
careful that the end of your rule is PERFECTLY CLEAN, be- 
cause otherwise it might leave a faint mark on the lens which 
would injure the definition of the picture on the screen. 

These tables do not appear very imposing, but you may 
take it from me they represent a vast amount of labor. I 
would not presume to claim perfection for them. In fact I 
think it quite possible they may be subject to improvement, but 
I do think they are the first really intelligent step in advance, 
in this particular direction, since the projection optical system 
was first evolved. 

I believe a great many operators are now losing a large 
percentage of their light by reason of the fact that the diam- 
eter of their objective lens is too small for the condition 
under which it works. You will observe, too, that the smaller 
the diameter of the lens the farther away must the conden- 
ser be from the aperture, and Table 2 will show you that 

Plate 18, Figure 63A. 

under certain conditions the arc will be a great distance 
from the lens, thus involving excessive light loss. If you 
are obliged to locate the arc more than 3 l /2 inches from the 
condenser in order to have a normal spot \ l /2 inches in diam- 


eter, and still meet the conditions as per Table 1, you may 
instantly conclude that something is wrong, and that some- 
thing most likely is one of two things, viz.: wrong condenser 
focal length or wrong diameter of the objective. Table 2 gives 
objectives up to 3 inches. Personally, I believe 2^ should be 
the limit. 

Plate 18 is a photograph of light rays obtained by 
placing a metal diaphragm, containing in its center a hole 
one-quarter inch in diameter, against the front condenser, so 
that the hole comes opposite to its center. You will observe the 
light ray conies down to a fine point, and the least diameter of 
the ray indicates the point at which the shutter should be set. 
In very long and very short focal length lenses it is impossible 
to set the shutter at this point because in one instance it comes 
inside the hood of the lens barrel and in the other it is so far 
away that the shutter cannot reach it. This point may be found 
by using a plate as in the foregoing and with the machine gate 
open blow smoke in the ray in front of the objective, whereupon 
the correct or at least the best position for the shutter can be 
plainly seen. 

Some men could 
learn if they didn't 
already know it all 



PROJECTION is a term which, taken as a whole, involves 
many things. As a matter of fact, broadly speaking, 
we may say that the whole motion picture industry 
rests to a large extent on projection. I base this statement 
on the fact that, no matter how perfect may be the work of 
the producer, no matter how beautiful may be the decora- 
tion of the theatre, or how excellent its appointments, or 
how courteous its attendants, or how perfect its music, still, 
if the projection of the picture itself be inferior the whole 
thing will necessarily be unsatisfactory and in considerable 
measure second rate. 

To put perfect projection on the screen, and maintain it 
perfectly during even one entire reel, requires ability of no 
mean order, as well as ceaseless vigilance, and some con- 
siderable degree of artistic sense. Not only must the projec- 
tion machine be kept in perfect condition, in order that there 
may be no unnecessary movement in the picture, no breaking 
of the film, or other faults due to a worn or badly adjusted 
mechanism, but also the light must be pure white, brilliant, and 
distributed over the aperture with perfect evenness, so there 
will be no shadow on the screen, other than that of the photog- 
raphy itself, and no discoloration of the light, except that caused 
by some fault in the film itself. 

It requires close study and considerable experience on the 
part of the operator to be able to determine accurately and 
at a glance whether a faint shadow or discoloration of the 
light is due to fault in the light itself or to fault in the film. 
The operator who proposes to deliver perfect projection 
must observe and compare closely. He must study projection 
from all points of view, and above all things must never 
arrive at the point where he imagines there is nothing more 
for him to learn. When an operator arrives at that point 
he; will cease to advance in his profession. The high-class 
operator who produces high-class results on the screen can 
seldom tell you, except in a very general kind of way, what 
a film portrays, even after he has run it several times. His 
whole attention will be taken up in constantly watching for 
faults in the light, gauging the speed of the projector to suit 
the action in each scene of the film, and attending to other 
things in connection with his projection. 


And now at this point let me say a few words to managers. 
In the olden days, so the Good Book says, Pharaoh ordered 
his Hebrew slaves to make bricks when there was no straw. 
The Hebrews could not do this, because, the way bricks 
were made in that ancient day, straw was a necessary part 
of the proceedings. There are, in this and other countries, 
many hundreds or even thousands of motion picture theatre 
managers who are emulating the example of Pharaoh. They 
are ordering their operators to produce high-class results 
on the screen but failing to supply them with the necessary 
things with which to do it asking them to "make bricks 
without straw." 

The manager who expects his operator to go up into a 
little 6 by 7 unventilated sweatbox, containing an old style, 
worn out (or not worn out for that matter old style is 
enough) projection machine, and produce high-class results 
on the screen, is expecting more than he is going to get. It 
is not in the nature of things and cannot be done. Yet 
many managers not only do this, but add insult to injury by 
refusing to purchase necessary repair parts, by doling out 
carbons one or two at a time, and, in general, making it 
utterly impossible for their operators to do their work in 
creditable fashion. 

There is another type of manager who will, in the begin- 
ning, provide a fairly good operating room and up-to-date 
equipment, but having done this much considers his duty as 
wholly finished. These projectors, to his way of thinking, ought 
to run twelve hours a day for the next six years without even 
so much as a new intermittent sprocket. He is generous in his 
advertising, spares no expense in film service, and is, in fact, 
liberal in everything except the matter of operating room ex- 
pense. Of course, it follows that, under these conditions, his 
operator is not going to and, in fact, cannot produce high -class 
results on the screen. 

These managers, too, frequently go even further than this 
in their foolishness, and, instead of employing the best opera- 
tor obtainable, paying him at least a fair salary, get the very 
cheapest man they can find. Any one who can twist a crank, 
splice a film and get some sort of a picture on the screen is, 
in their opinion, an operator, provided he is cheap enough. 

The wise manager, the manager who succeeds in any large way, 
is the one who employs the best operator he can get, provides 
him with decent working quarters, up-to-date projection machin- 
ery, and says: "Now see here, Mr. Operator, within reason you 
may purchase anything you want in the way of supplies. If I 


catch you wasting you will be promptly fired. I only look to 
you for one thing, and that is results on the screen, but it is re- 
sults I want, not excuses" 

The manager who takes this position is entitled to results 
on his screen, and he is of the type of man who is going to 
get them, too. 

But to get back to our subject. When the operator is in 
doubt as to whether some faint shadow or discoloration on 
the screen is due to the light, or to some fault in the film 
itself, the matter may be determined by shifting the lamp 
a trifle. If the shadow or discoloration remains unchan'ged 
as the lamp moves, it is due to some inherent defect in the 

Discoloration or shadows due to light fault are detected 
by observing white or light colored objects in the picture. 
A white dress, for instance, must be pure white all over. If 
a woman is in the foreground and the bottom of her white 
skirt is in any degree yellow, the rest being pure white, it 
means that your light is in need of instant adjustment. Very 
likely the arc is too long. If the discoloration appears at 
some other point in the picture, it means the same thing, viz., 
the light requires adjustment, assuming, of course, your 
lenses are properly matched, so that you can get a clear, 
white screen. It is not the purpose of this work to tell the 
operator each separate adjustment to make to overcome or 
correct every separate fault. This he must learn for him- 
self, by experience. He is presumed to have brains. If he 
has not a goodly quota of that highly desirable article he 
has no right place in the operating room. Jf he has brains, 
and uses them, he will quickly learn how to adjust the light 
to correct the various faults. 

When the operator is allowed to use sufficient current; is pro- 
vided zvith good carbons and the right lenses, there is ordinarily 
no excuse for any shadow or discoloration of the light. 

It may be stated as a matter of fact that with modern 
films of the best makes it is quite possible to project a 
motion picture which will be to all intents and purposes 
absolutely free from movement and absolutely evenly and 
brilliantly illuminated. This, however, can only be done by 
a high-class operator who has at his command ample cur- 
rent, high grade carbons, and a carefully selected, up-to-date 
projection machine. 

This, however, must be qualified by the statement that 
there are only a few makes of films which are to all intents 
and purposes so mechanically perfect in their perforations 


that even a perfect projector will put them on the screen 
without some movement. In fact, there are none so perfect 
that there is no movement at all, though the European Pathe 
and a few American producers are now very close to the 
ideal in this respect. 

Speed of Projector. The speed at which the film is run is a 
matter deserving of the closest study and attention on the part of 
the operator. There are those who insist that some overspeeding 
of the projection machine lends "snap" to the picture on the 
screen. This opinion is held by no less person than Mr. S. L. 
Rothapfel, manager of the Rialto Theatre, New York City. 
Also Mr. D. W. Griffith, who produced that marvelous production 
"The Birth of a Nation," holds that it is desirable to overspeed 
the film. With this view, however, I am unable to agree. I take 
the position that the actors who enact scenes in films are presumed 
to know their business, and to enact the scenes in the best pos- 
sible way. If this be true, then overspeeding of the projector com- 
pels the shadow-actor to enact a scene quite differently from the 
way it was done in real life. Hence if the speeded shadow scene is 
right, the real scene was wrongly enacted, and vice versa. I have 
never yet been able to see a horse, for instance, moving across a 
screen at a speed at which no horse could possibly move in real 
life, and be satisfied, and I think no one else is really satisfied with 
that sort of thing. I am a firm believer in the fact that an ex- 
ceedingly important part of the operator's work is to carefully 
gauge the speed of his projector, so that the figures in the various 
scenes will move in an absolutely lifelike manner, and this, when 
you come to think of it, means a great deal. It means that the 
operator must know exactly what "lifelike manner" is, which 
involves a close study of many things. 

Of course if cameramen always ran their cameras at ex- 
actly 60 feet per minute, all that would be necessary in 
order to reproduce a scene on the screen precisely the way 
it was acted would be to run the projector at 60 per minute. 
As a matter of fact, however, cameramen, while they are 
presumed to run at exactly 60 a minute, don't do anything 
of the sort. Suppose one cameraman misjudges his speed 
and runs at 58, or two feet under normal, whereas the 
cameraman taking the next scene misjudges his speed in 
the other direction, and runs at 62. Now if the projection 
machine pounds along at 60 a minute, one scene will be 
run too slow and the other too fast, or if the whole thing be 
run at either 58 or 62, one scene will be correct and the other 
very far from right. 


The operator who thinks that the finer details of projection are 
not of sufficient importance to justify him in giving them atten- 
tion is not and never will, in my opinion, be a high-class man. 

It is quite true it usually is a difficult and discouraging 
task for the operator to secure recognition for high-class 
work. In fact, many managers' won't let him deliver high- 
class work, but, nevertheless, the man who persistently and 
consistently bends his energy to improving his projection 
in every possible way is, I think, bound to win out sooner 
or later. High class work cannot but be noticed. It may take 
considerable time; it may be discouraging, but success will 
come, and with it, at least in some degree, financial reward. 

Almost the same thing may be said of the manager. The 
manager who employs a high-class operator, pays him an 
adequate salary, provides him with good working conditions, 
tools and supplies, and insists on high-class projection, may 
not immediately see the benefit. Nevertheless the public in 
due course of time will recognize the fact that in a certain 
theater they are sure to see a good picture, and, other things 
being equal, they are going to patronize that theater. 

Overspeeding the Machine. Overspeeding the machine is 
a reprehensible thing from any and every point of view. It 
is an all too common fault, practiced by managers of theaters 
who have no respect for the property intrusted to their care 
by the film exchange and no adequate conception of the 
business of exhibiting motion pictures or their duty toward 
their patrons. There is a certain type of manager who seems 
to have an ingrowing idea that the public collectively is a 
fool; that it would rather see six reels put on the screen 
as a ridiculous travesty on projection as an absurd jumping- 
jack performane, than see five reels put on the screen right. 
They insist on shooting a reel of film through in less time 
than is required for its proper projection. There are man- 
agers who will talk to you learnedly about a reel requiring 
"fifteen minutes," or "eighteen minutes," according to their 
individual ideas. They have no adequate knowledge of pro- 
jection themselves, and don't understand the fact that, whereas 
one reel cf film may require only fifteen minutes (nine reels 
out of ten will require more time than that), another may 
require as much as twenty minutes; both fifteen and twenty 
being extremes. Many "managers" insist on putting on a 
six-reel program in the time that ought to be consumed by 
five reels. Over on the east side of New York City I have 
actually seen one thousand feet of film projected in considerably 
less than ten minutes. 


Overspeeding the machine is an outrage on the public; an out- 
rage on the producer; an outrage on the film exchange; an out- 
rage on the projection machine manufacturer, and an outrage on 
the operator himself. There is no excuse for it absolutely none 
at all. If the house is full and a crowd waiting to gain entrance 
it would be far better to cut out one reel than to injure the whole 

The operator is very seldom to blame for this particular 
thing. Nine times out of ten it is the manager himself who 
commits what amount to a crime against the business, when 
he orders overspeeding of the films. A film might be run 
at the rate of 70 feet (70 turns of the projector crank) per 
minute without undue strain to the film, but if long con- 
tinued it will inevitably injure the projection mechanism. If 
one will but pause and consider: There are sixteen pictures 
to each foot of film. Each picture must stop dead still over 
the aperture, and then be displaced by the next one after 
exposure, all in one-sixteenth of a second when running at 
normal speed. This means that the strip of film between 
the upper and lower loops must start and stop sixteen times 
each second. If the crank speed be increased to 70 per 
minute it means that this stoppage and starting must take 
place at the rate of nineteen per second, instead of sixteen. 

At 80 turns of the crank per minute it means that twenty- 
two pictures (almost) will be exposed each second. Not 
only must the strip of film between the two loops be started, 
against the considerable pressure of the tension springs, at 
this terrific speed, but also the intermittent shaft, star and 
sprocket must also be started and stopped at the same rate. 
It requires but slight knowledge of mechanics to understand 
the strain thus placed on the sprocket holes of the light, 
fragile film, as well as on the intermittent movement of the 
projector. Overspeeding also makes necessary a tighter 
tension, which still further aggravates the damage. The 
camera which took the scene is supposed to run at 60 a 
minute. Films and projection machines are intended to 
withstand the strain of 60 a minute and will do so. When, 
however, this speed is exceeded to any considerable degree 
the strain multiplies rapidly, and the consequent wear and 
tear is several times what it is at normal. 

Effect of Loss of Definition. One factor enters very 
largely into projection which is very little understood by 
the average manager and operator. This matter has been 
called to my attention by Mr. Nicholas Power of the 



Nicholas Power Company, and while I have never thought 
of it in that connection before I believe Mr. Power is ab- 
solutely correct. 

Patrons frequently complain that "pictures hurt their eyes," 
even when there is no trace of flicker. Managers and oper- 
ators have been puzzled 
to account for this. Mr. 
Power's explanation of 
the matter is as follows : 
Take a carbon copy of 
a letter or long article, 
and attempt to read it. 
You will find that before 
you have read very far 
your eyes begin to hurt 
and even to water. The 
reason for this is found 

in the blurry appearance \ Figure 64. 

of the copy, and the 
more blurry the carbon the greater will be the strain on the eye. 
The same holds true with pictures. If the definition on 
the screen be not absolutely sharp, the effect on the eye is 
a strain, and not only is this effect present where there is 

lack of definition 
through fault of the 
camera or the pro- 
jection lens, but it is 
also present where 
there is a travel ghost. 
This, it seems to 
me, is an important 
point, and, moreover, 
it is a new point. I 
believe this is the 
first time it has re- 
ceived consideration. 
I would advise man- 
agers to look into 
this matter and to 

use every endeavor to have the definition on their screen as 
sharp as it can possibly be made and travel ghost entirely 
eliminated. Of course, we all know that from any point of 
view the loss of definition and travel ghost is bad, but viewed 
in this light it becomes doubly obnoxious. 

Figure 65. 


Side View. Many times the question has been asked: 
"Why do the screen figures .look abnormally tall and thin 
when viewed from a heavy angle?" This is clearly ex- 
plained in Fig. 64; in which two people, C and D, view a 
figure having a normal width of A-B on screen X = X. C 
gets the full benefit of this width, as per lines A-B, but D 
only gets the effect of width as per dotted line B-E, for 
reasons which are self-evident. 

Keystone Effect. Where the machine is set above the level 
of the screen the bottom of the picture will be wider than its top, 
thus producing what is known as "keystone effect," as shown 
at H, Fig. 65. This effect is due to the fact that the light 
ray spreads out as it travels, and to the further fact that it 
must travel farther to reach the bottom of the screen than it 
must travel to reach the top when the angle of projection is 

This is illustrated in Fig. 65, in which A is the lens of 
the projector, B-S the screen and F-S the horizontal distance 
of projection, H, being a detail to show shape of picture 
under these conditions. If the top of light rays A, B, S, are 
all to travel the same distance to reach the screen, then the 
screen would necessarily be located at B-D, and the picture 
would have its normal shape, but since the bottom of the 
screen is at S, it follows that to reach the top of the screen 
the light rays must only travel from A to B, whereas in 
order to reach the bottom it must travel from A to S, or the 
distance D-S in excess of distance A-B. Now assuming A-B 
to be 60 feet and the top of the picture to be 15 feet wide, and 
the distance D-S to be 3 feet, we would have a light ray which 
spreads 15 -^ 60 = .25 of a foot, or 12-f-4 = 3 inches with 
each foot of throw. Hence it follows that distance D-S 
being 3 feet, the width of the bottom of the picture would 
be 3X3 = 9 inches greater than the width of the top of the 
picture. The same thing as applied to a 40, 30 and 15 degree 
angle on an 80-foot throw is fully illustrated in Fig. 66. 

The same condition prevails when the machine is set to one 
side of the center of the screen, except that in this instance 
the keystone effect will be sidewise that is to say, one side 
of the picture will be higher than the other side. There is, 
however, this difference: The up and down keystone effect 
is, for some reason which I have never been able to under- 
stand, never accompanied by as great a tendency to out-of- 
focus effect as is the side keystone. The instant the machine 
is set to any considerable distance to one side of the center 
of the screen difficulty is encountered in getting a picture 



Figure 66. 


which is sharp all over, and if the machine be set much to 
one side it will be found practically impossible to get even a 
reasonably good picture. It is no unusual thing, however, to 
have a machine giving a fairly sharp definition all over the 
picture with a drop in projection of fully 40 feet in 100. Of 
course a portion of this difference in effect is accounted for by 
the fact that the picture is wider than it is high, but this does 
not seem to explain the whole thing, as a fairly sharp picture 
may be had with very steep downward pitch. 

The keystone effect, so far as the outline of the picture is 
concerned, may be corrected by filling in the projector 
aperture with hard solder, and then carefully filing it out 
until the picture assumes its normal shape on the screen. 

The best and in fact the only practical way to do this is to 
fill in with solder and file the aperture to shape when the 
light is on, first, however, having removed one of the con- 
densing lenses so that the spot will be very large, since other- 
wise it will be too hot to work in. By this method you can 
watch the exact effect of every stroke of the file upon the 
outline at the screen. Be very careful that you do not get 
a little too much off, because if you do you will have to do 
the whole job over again. If the machine sets above the 
screen the filing will have to be done on the sides of the 
aperture, the lower part of the aperture being made widest. 
If the machine sets to one side of the screen then the top 
and bottom will have to be filled in. Before beginning, hang a 
narrow strip of black tape, weighted at its lower end, with its 
upper end just where the lower end of the upper corner bend 
comes. This will supply guides so that you will get the side 
lines perfectly straight and perpendicular. Bevel the sides of 
the aperture opening slightly on the screen side. 

As before stated the outline of the picture can be corrected 
in this way, but the distortion of the picture will remain. 
That cannot possibly be corrected, except by setting the 
machine lens central up, down and sidewise, with the center 
of the screen. 

The out-of-focus effect which accompanies keystone effect 
where the machine is set to one side of the center of the 
screen may, if it be not too great, be corrected by loosening 
the aperture plate and placing a thin strip of metal under 
one side, the idea being to slightly raise one side of the 
aperture plate, provided it be a type of machine which will 
allow of its gate being squared with the aperture in its new 
position. Up and down keystone effect can also be corrected by 
blocking the upper end of the aperture plate out somewhat ; but 


this cannot be carried very far, or trouble with the tension shoes 
will be encountered. 


(Also see Limit of Amperage, Page 292.) 

The number of amperes to be used for the projection of a 
given size picture depends, to a large extent, on the screen 
surface used and the kind and amount of auditorium light- 
ing; 'the percentage of light cut by modern projectors vary- 
ing but little from 50 per cent. 

There are still those who commit the error of assuming 
that the 'distance of projection (throw) has much to do with 
the necessary volume of light; also there are still those who 
attempt to apply the well known law that "light intensity 
diminishes with the square of the distance." 

Let me again correct these impressions. Provided the 
lens system of the projector be properly matched, it makes, 
within reasonable limits, but very little if any practical 
difference what the distance of projection is. With the 
arc at a given distance from the condenser a certain amount 
of light is distributed over the area of the spot, and a cer- 
tain percentage of this light intensity passes through the 
aperture of the projector and, of course, the film. If the lens 
system is properly matched, practically) all light passing 
through the film will enter the objective lens; also practically 
all light entering the lens will leave it (I am laying aside, 
for the time being, the absorption of light in passing through 
glass); and, once having left the lens, a moment's thought will 
convince even the most skeptical that if a ray of light can 
travel ninety-three millions of miles from the sun to the 
earth, a difference in distance as between 50 and 100, 150 or 
even 250 feet is not going to make any practical difference, 
provided the atmosphere be even reasonably free from dust 
and smoke, which would cause more or less diffusion. 

In Fig. 67 we see an illustration of the law : "Light in- 
tensity decreases inversely with the square of the distance." 
In this illustration A, B and C represent different positions 
of a screen. Light rays emanating from a central source 
travel in straight lines in all directions. It requires but a 
glance to see that, this being the fact, these light rays will 
spread fanwise as they travel, and that in position C the screen 
would receive only a comparatively small percentage of the 
light it would receive if it were in position A. In fact, 
screen B would have to be as large as is indicated by the 


dotted lines in order to receive the same total illumination 
received by screen A, which would, of course, greatly re- 
duce the brilliancy per unit of area, and screen C would need 
to be still larger in order to catch the same number of rays 
screen A receives. This is a very plain illustration of the 

Figure 67. 

law in question, but this law does NOT apply to projection, 
except in a very modified fashion. 

In a projection machine we have an arc lamp with the 
crater forced into a position where it will face the con- 
densing lens as squarely as possible. By reason of this 
condition a certain given and very high percentage of the 


light emanating from the crater on the carbon strikes the 
rear surface of the condensing lens, and is by that lens 
projected to the spot, where again a certain definite per- 
centage passes through the aperture of the machine. Now 
the light which passes through the aperture and film passes 
on and into the objective lens, where it is given a certain 
definite direction. The rays do not spread out in every direc- 
tion, as per Fig. 67, but only on the lines determined by the 
curvature of the lens, therefore the light intensity of the screen 
is proportional to the total candle power of the light ray at the 
front end of the objective lens as compared to the area of the 

Loss of Light in Lenses. At this point it is, I think, 

proper briefly to consider the loss of light in the lens system. 
It is a well known and established fact that, in passing 
through glass, light loses .a certain proportion of its intensity. 
This loss has been variously estimated by different authors, 
but it appears to me the conclusion arrived at by Mr. J. 
Frank Martin, of Pittsburgh, Pa., in a paper entitled, "The 
Illumination of Motion Picture Projectors," read before the 
Pittsburgh section of the Illuminating Engineering Society, 
April 18, 1913, is the first and only authoritative statement 
concerning the loss of light in the lens system of a projection 

I would not by any manner of means wish to be under- 
stood as indorsing the conclusion arrived at by Friend 
Martin. In fact, it seems to me those conclusions lead to an 
impossible screen effect, but, nevertheless, as I before said, 
they are the only authoritative statements I have ever seen 
on the subject. Mr. Martin says, in part: 

"Many different combinations of lenses have been experi- 
mentally developed, but no radical changes have been made 
from the earliest form used in the magic lantern. The lens 
system and the losses therein are illustrated in Fig. 68. 
The projector lens system has been built up with a point 
source of light as a basis; hence the low efficiency of 10 per 
cent, is not surprising, and there is apparently great oppor- 
tunity for improvement." 

The diagram will be of great interest to operators; also 
it will have for him some surprises. However, I do not 
think the right impression is conveyed when Mr. Martin 
says there is an efficiency of 10 per cent, at the screen. This 
does not seem to me to be a fair statement of fact. As I 
understand it, Mr. Martin assumes an efficiency of 10,000 c.p. at 



the arc, meaning by this that the surface of the crater itself has 
a total light efficiency equal to 10,000 c.p., but after the rays 
have spread and a portion of them have been lost in the 
interior walls of the lamphouse, there remains only an 
efficiency of 200 c.p. at the surface of the front condenser. 

i*v ne#cf#r 70 


Figure 68. 

Now what I understand this to mean is, in effect, that if the 
area of the crater could be magnified to the size of the con- 
denser and, without considering the light loss in the interior 
lamphouse walls, it still, as a whole, gave off 10,000 c.p., the 
light giving power per unit of area would be reduced to 200 
c.p., or, putting it in another way, the diminution of light 
intensity per unit area of measurement amounts, by reason 
of the spreading of the light rays, to a difference between 
10,000 and 200. 

And now comes something that will be mighty interesting 
to the average operator, viz., the loss of 70 per cent, in the 
condenser itself. This loss Mr. Martin holds is, to a con- 
siderable extent, due to the use of low grade glass in cheap 
condensing lenses. The lenses used in the test were a pair 
of 6 l /2 and 7 l / 2 plano-convex, of the ordinary variety. The 
test was made with a Sharp-Miller photometer, by placing 
a standard test plate at the point where it was desired to 
measure the brilliancy. This test plate is a smooth, white 
surface which reflects a definite proportion of the light from 
its surface. By placing such a test plate flush with the sur- 


face of the condenser, next the arc, and measuring the light 
reflected therefrom, it was found that 200 c.p. was the 
brilliancy of each square inch of the condenser surface. The 
arc had been previously adjusted and placed in a position 
that gave a clear, round spot at the. aperture of the machine. 
When this test plate was moved to the surface of the outer 
condenser, and the indication taken in the same manner, 
60 c.p. per square inch was the light intensity recorded, which 
indicates the astonishing loss of 70 per cent, in the con- 
denser itself. This does not, at first blush, appear to be 
reasonable, nor do I believe it represents exactly the fact, 
because a slight alteration in the length of the arc may (I 
don't say it would, but it might) affect a considerable differr 
ence in the quality of the light, which might operate to 
diminish its brilliancy. Nevertheless, whether the figures 
are accurate or not they certainly do show that the con- 
denser absorbs an enormous percentage of the light. Nor 
are we altogether surprised that this is the fact when we 
remember that the thin filament of glass contained in an 
incandescent light globe causes a loss of 3 per cent. You 
would hardly think this latter were possible, but illuminating 
engineers tell us it is the fact. 

This tremendous condenser loss certainly points to the 
enormous importance of using high class condensing lenses 
the best that can be had, and even then the loss would be 
very great. The inefficiency of the condensing lens was very 
thoroughly proved to the writer when he witnessed the 
demonstration of a parabolic reflector designed to concen- 
trate the light without the use of condensing lenses. He was 
literally amazed to witness the projection of a really 
brilliant, beautiful sixteen-foot picture with only slightly in 
excess of 12 amperes of current, using an ordinary muslin 
screen. This reflector, or light concentrator, has never as 
yet been got into a form where it is practical for general 
motion picture work, but it did show the tremendous gain 
which would be made possible if the condenser could be 
eliminated. Moreover, the light had a white, mellow, pleasing 
quality the writer has never seen in an illumination which has 
passed through condensing lenses. 

But to return to our subject. Referring to Fig. 68, we 
find that the test plate, when placed at the aperture of the 
machine, showed a brilliancy of 510 c.p. per square inch, but 
that immediately after the light had passed through the film 
only 470 c.p. was shown, which indicates a loss of 8 per cent, 
in the film itself. The film used was a clear piece from which 


the photographic emulsion had been removed. Therefore 
it appears that the celluloid of the film itself absorbs 8 per 
cent of the light. 

And now comes the point which makes this whole thing 
appear to me as rather impossible, except viewed from the 
standpoint of proportiotls of loss. It seems to me that, if 
the aperture had an area of one square inch, and the light 
brilliancy passing through it were only 470 c.p. per square 
inch, then the screen itself could only have a brilliancy per 
square inch equal to 470 divided by the total square inch area 
of the screen, which would give us an actual screen brilliancy 
of only a very, very small fraction of one candle power. As 
a matter of fact even that result would be too high, because the 
area of the aperture is only about three-quarters of one square 
inch, therefore the real screen brilliancy would be three- 
quarters of 470, divided by the square inch screen area, and 
even that} would be reduced by the 8 per cent, loss in the 
objective lens. 

I have given this matter space because of the fact that it 
points an entrance to 'a road which needs thorough explor- 
ing, and needs it badly, too. The projection lens itself, 
being of very high grade glass, only entails a loss of 5 to 12 
per cent., averaging, Mr. Martin says, 8 per cent. The thin 
bulb of an incandescent lamp, made of ordinary glass, causes 
a light loss of 3 per cent. Now the total glass in the two 
combinations of the ordinary projection lens will, I think, 
measure about five-eighths of an inch in thickness. If it is true 
that less than one-thirty-second of an inch of ordinary glass 
causes a light loss of 3 per cent., and approximately five- 
eighths of an inch of very high grade glass causes a loss 
of only about 8 per cent., it would seem to be readily apparent 
that there would be an enormous gain in using very high grade 
optical glass for condensing lenses. 

It is but a step from this result to the inevitable conclusion 
tbat there is a huge duty devolving upon machine manu- 
facturers to evolve some method of absolutely stopping the 
breaking of condenser lenses, to the end that really high- 
class, expensive ones may be used. Already the Elbert and 
Preddy condenser holders have paved the way. Altogether 
too little attention 'has been paid to this extremely important 
matter in the past. 

To get back to our main subject. Broadly speaking the num- 
ber of amperes necessary to produce a given curtain illumination 
will depend upon the number of square feet contained in the 
screen, the character of surface of the screen and the percentage 


of light cut by the revolving shutter. As set forth, the modern 
projection machine will, under the best conditions, cut approxi- 
mately 50 per cent, of the light, and under adverse conditions 
may cut somewhat more than this, though the variation either 
way from 50 per cent, will be but little. The area of the screen, 
and the character of its surface, however, are largely governing 
factors. Suppose we are projecting a picture 8 by 10 feet at 60 
feet. In a space 8 by 10 feet are 80 square feet of surface. Now, 
understanding that practically all light rays leaving the objective 
lens reach the screen, while light rays are really numberless, let 
us suppose, for purpose of illustration, that we have exactly 160 
rays of light leaving the projection lens. This would, of course, 
mean that each square foot of screen would be illuminated by 
just two rays of light. 

Now suppose we change our lens to one projecting a picture 
12 by 16 feet, which would have 192 square feet of surface. The 
total light remains the same, but the surface has been more than 
doubled. It therefore follows that the light, being spread over 
more than twice the area, has been weakened, so far as screen 
illumination be concerned, by more than one-half. Where we 
formerly had an illumination equal to that produced by two rays 
for every square foot of screen surface, we now have an illu- 
mination less than that equal to one ray to, the square foot. We 
still have exactly the same total amount of light, but have, in 
limited degree, invoked the law of inverse ratio already spoken of. 

We thus see that illumination decreases as the area over which 
it is spread is increased. It therefore follows that if the size of 
the picture (area) be increased, it will be necessary, in order to 
maintain the same brilliancy, that the power of the light, or, in 
other words the amperage, be also increased to a value which will 
supply to each square foot of screen surface the same intensity 
of illumination it received in the smaller picture. 

In the second edition of the Handbook I gave an amperage 
table which was presumed to be satisfactory for use with any 
good, non-reflective screen, such as a plaster wall, calcimine 
surface, white muslin, etc. I see no reason for making any 
changes in this table, except to say that the modern tendency is 
for more brilliant illumination, and this would increase the 
figures given, I believe, by very nearly 25 per cent. In other 
words, high-class theatres of today would probably use nearer 50 
amperes than 38 on a 15 foot picture. I shall, however, give the 
tables unchanged, but with the foregoing modification. Those 
who wish to follow up-to-date practice are recommended to 
increase the amperage given by 25 per cent. In the "Amperes 
A. C." column of the table I have made 60 amperes the limit 


this by reason of the fact that operating room transformers 
(compensarcs, inductors, economizers, etc.) almost without ex- 
ception have a 60 ampere maximum capacity. As a matter of 
fact, however, not less than 90 amperes A. C. should be used on 
a 20 foot picture and an 18 foot picture should have not less than 
75 or 80. Where A. C. is u^sed on large pictures I would recom- 
mend two economizers wired in multiple. The figures given 
in the table are based on the presumption that the screen surface 
is in good condition. 


Amperes Amperes 

Picture. Area Sq. Ft. D. C. A. C. 

6.75 x 9 61 20 35 

7.5 xlO 75 20 35 

8.25x11 91 20 35 

9 x!2 108 22 35 

9.75x13 127 25 38 

10.5 x!4 147 29 44 

11.25x15 169 33 50 

12 x!6 192 38 58 

12.75 x 17 216 43 60 

13.5 x!8 243 45 60 

14.25x19 268 45 60 

15 x20 300 45 60 

Another governing factor in j the matter of amperage is the 
type of screen surface used. There are on the market a 
number of semi-reflective so-called metallic surf ace screens, 
and one make of glass surface screen. The principal value of 
these screens lies in, the fact that a greater curtain brilliancy 
may be obtained with a very considerable less current con- 
sumption than is necessary with the non-reflective screen 
surfaces. This matter will, however, be dealt with more 
extensively under the heading "The Screen," Page 166. 

We have learned that screen brilliancy will not depend up- 
on the total amount of , light projected to the surface of the 
screen, but upon the total amount of light projected to each 
square foot of screen surface. This brings us to the inevitable 
conclusion that 

A certain given amperage per square foot of screen surface will 
give a certain definite brilliancy of illumination to the screen, 
other things being equal. 

There are, of course, many equations, entering in less degree 
into this matter. We are only speaking in generalities. For 
instance, curtain brilliancy will to a certain extent depend 
upon the set of the carbons and the angle of the lamp, but 



at this stage; of affairs even the tyro operator is supposed to 
have a fairly good knowledge of carbon setting and lamp 
angle, since there is but one correct 'setting and one correct 
angle, modified only to some extent by the pitch of the pro- 
jection , machine itself. 

The amperage will also depend, to some slight extent, on 
the clearness of the atmosphere, to a considerable extent 
and 'amount on the auditorium lighting, upon the density of 
the film, upon the grade of lenses used, and the matching of 
the optical system. All these are more , or less potent fac- 
tors, and no set rule can be given, nor can any table be 
given which will meet all conditions. 

The following very interesting table shows the increased 
percentage of light made necessary, by increasing the size 
of the picture, for instance: If you have a six foot picture 
and desire to .increase it to seven feet: The area of your 
six foot picture is 26.4 and the area of your seven foot pic- 
ture is 35.9 square, feet, an increased area of 9.5 square feet, 
which will require 36 per cent more light. In other words, 
to illuminate a seven foot-, picture to the same brilliancy as 
a six foot picture would require 36 per cent more light. The 
percentage, however, decreases as the size of the picture 
increases; that is to say, there is a less percentage between 
the ten and thirteen foot than between the eight and twelve 
foot picture. This table ought to form a very interesting 
study for operators. It Js based on the fifteen-sixteenths 
inch aperture. 


in feet. 





in feet. 
















sq. feet. 
















Area increase 
in sq. feet. 



of increase 





The Screen 

THE particular and only function performed by the 
screen of a moving picture theatre is to reflect "picture 
light." We see the picture precisely for the same 
reason that we see any other object. As light rays are re- 
flected from various objects to the eye, so, in projection, light 
rays reflect from the screen to the eye. The picture appears 
plainer, sharper and better if "picture light" alone is reflected 
and if the "picture light" is abundant. 

There is very great difference in screen surfaces and in 
results from the various surfaces, yet IT is UTTERLY IMPOSSIBLE 


THE OTHER. It is impossible to properly judge of screen surface 
values by looking at screens in different theatres, by reason of 
the fact that there are seldom or never two screens in neighbor- 
ing houses where all factors are equal and the working con- 
ditions are precisely alike. The brilliancy of the projection 
light may be different, due to (a) difference in amperage, 
(b) in carbon set, (c) in carbons, (d) quality of current, 
(e) machine shutter. Also general results may be altered 
by difference in the decoration of the theater auditorium; in 
the border surrounding the screen; in the length and width 
of the theatre; in the distance of the screen from the audi- 
torium proper; in the size of the screen; in the angle of the 
throw, or in other things. In fact these many and varying 
equations make it absolutely impossible to realize the true 
value of a screen surface by the plan of going from one 
theatre to another, depending on the eye alone to judge 
relative values. For example, changing from a small screen 
to a large screen will cause the "picture light" to appear, by 
comparison, less brilliant, assuming other conditions to be 
equal in both cases. A change from a screen of 100 square 
feet area to one of 200 square feet area will cause the large 
screen, if the two surfaces be alike, to appear 50 per cent, 
less brilliant than the smaller. 

It is even impossible accurately to judge of different screen 
surfaces by projecting a picture on one screen and then sub- 
stituting the other therefor, projecting upon it the same 
picture. This by reason of the fact that the light may not 
be the same. Something may have happened to drop the 
supply voltage slightly, which would effect the amperage at 


the arc, and hence the light. The operator may not have his 
carbons adjusted precisely the same in both instances, which 
would or might cause a change in the screen brilliancy. In 
view of these facts the only right way is the one I have sug- 
gested. That kind of test is absolutely fair to everybody 
and it is not a difficult one to make either. 

I would most emphatically warn the operator and manager 
of the danger of judging hastily as between screen sur- 
faces. I would also caution managers and operators against 
the too ready acceptance of the statements of salesmen as 
gospel truth. Salesmen are employed to sell goods, and some of 
them, I am sorry to say, don't always confine themselves to 
statements which the facts will bear out. 

As a matter of fact I now have an instance before me in 
which an exhibitor paid $75.50 for a screen. It was a good 
screen, too, the surface being guaranteed for five years. But 
not very long after it was installed along came a nice, smooth- 
talking artist, in the shape of a salesman for another brand of 
screen. Now this other brand of screen was not one iota 
better, even if it was really as good, as the screen the man 
already had, yet, as absurd as it seems, the salesman actually 
talked the manager into paying $225 for a new screen. The 
part of this which makes the transaction particularly dis- 
honest is the fact that the new screen could unquestionably 
have been sold at a good profit for the same price he paid 
for his other one, viz: $75.50. Verily there seems to be a 
new sucker born every minute, and some of these are found 
in moving picture theatre managerial capacities. 

The time will, I presume, come when the screen business 
will settle down to a solid basis, and some type of screen 
surface will be found to be best and become standard. At 
the present time, however, I cannot do more than point out 
to theatre managers and to operators the necessity for demand- 
ing that screen salesmen give them at least reasonable proof 
of the correctness of their statements, and that proof is best 
given by actual demonstration as before outlined. It is not at 
all impossible for a screen salesman to carry with him a 
sample surface large enough to cover half of any ordinary 
theatre screen. Make him hang the sample up over half of 
your screen and show you, always remembering that a new, 
clean screen surface is, of course, somewhat more brilliant than 
one you have been using for a year or two. Don't attempt to 
judge from a small sample, however. Make him cover one-half 
of your screen with his sample. 


As a matter of fact, when it comes right down to absolute 
accuracy, it would be necessary to build a screen to meet the 
requirements of each individual house, but this is, of course, 
impractical, nor would the added benefit justify the necessary 
amount of labor and extra expense involved. 

Light. As stated, the only function of the screen is to re- 
flect light. Therefore, in order to understand results emanat- 
ing from a certain screen surface we must first understand a 
few of the many laws governing light action. Light travels 
at the almost incomprehensible speed of 192,000 miles a 
second. This speed is such that we have no way of controlling 
it; therefore its speed cannot be altered. This is an item 
that is of no interest to the operator, except as a matter of 
general information. There are two kinds of reflection, viz: 

Regular Reflection and Diffuse Reflection. Regular reflec- 
tion occurs when light strikes a smooth, polished surface and 
is not broken up and scattered, as, for instance, the reflection 
from a looking glass. Example: We see ourselves in a 
mirror because light reflects from our face to the glass, and 
comes from the glass into our eyes without being scattered 
or diffused. 

Diffuse reflection occurs when light comes to the eye from 
a body which has a roughened, unpolished surface, which by 
reason of its roughness, scatters or diffuses the light rays. 

Reason for the Haze. Surfaces which have, to a certain 
extent, both the elements of polish and roughness, reflect 
both regular and diffuse reflection, and thus produces a haze, 
by reason of the fact that the regular reflection is superim- 
posed over or upon the diffused reflection. This is a pecul- 
iarity of the polished metallic screen surface, and explains the 
reason for the failure of many home-made metallic surface 

Light Travels in Straight Lines. Light rays travel from 
their source to a surface in perfectly straight lines, and when 
the light is reflected from a surface to the eye it again 
travels in perfectly straight lines, providing, of course, the 
air or space between be a perfectly transparent medium, of 
uniform density. Light may travel from one surface to an- 
other several times, and the direction of its rays change in 
each instance, but the traveling is, nevertheless, always, subject 
to change of density in the medium, in straight lines. 

When light strikes a roughened surface, the minute rough- 
ened elements, which we may term "peaks and depressions," 


will cause it to scatter and reflect in all directions. The direc- 
tion of the reflected rays depend upon the angle of these minute 
peaks or depressions, and upon their location with reference 
to the source of light. "Picture light" projected upon a 
screen is reflected from the screen into the eye from the vari- 
ous peaks and depressions upon the screen surface, and is 
scattered in a narrow or wide angle in exact proportion to 
their size. 

Peaks and Depressions. These peaks and depressions are 
small, and, as a general proposition, invisible to the naked 
eye. A single ray of light is of exceedingly small dimensions. 
Scientists tell us that a bundle composed of thirty-six light 
rays has the same area as that of an ordinary human hair. 
The peaks and depressions which scatter light may be just as 
minute as is the diameter of a light ray. It is not to be 
understood that I am referring to a surface so rough that 
the human eye can see the roughness. A surface may have 
a rough matte appearance, and yet the minute elements in 
that surface may be very smooth, and therefore not cause 
perfect diffusion of the light, whereas a surface which may 
appear smooth to the eye might be of such character that it 
would scatter light rays in all directions, and thus create per- 
fect diffusion. In other words light .rays and elements of 
surface that scatter light are both almost of an infinitely 
small dimension. 

Matte Surfaces. It must be understood that, given the 
peaks and depressions, as above set forth, there is an added 
value and a very decided added value if the surface of the 
screen be also visibly roughened, that is to say, if it be of a 
matte character. This matte or visible roughness is not an 
absolute necessity, provided the smooth surface be of the 
proper character, but it is nevertheless eminently desirable 
since it adds very materially in the production of a perfect 
picture. True, the matte surface has little or nothing to do 
with the actual diffusion of light, but nevertheless it per- 
forms another important function, in that it enables the eye 
to see the picture more clearly and in greater detail when 
viewed from a side angle. 

Interfering Light. One of the prolific causes of failure to 
secure clearness, brilliancy and beauty in the picture is what 
may be termed "interfering light." Interfering light is any 
light other than "picture light" which strikes the surface of 
the screen. It may be caused by (a) stray light beams from 
the operating room, which strike the wall or ceiling and are 


reflected to the screen. These rays usually emanate from the 
condenser; they can be and by all means should be elimi- 
nated, (b) Daylight, which is a most prolific cause of poor 
results at matinee performances. It is amazing how little at- 
tention managers and operators pay to the thorough excluding 
of daylight from the auditorium at matinee performances. Any 
daylight which reaches the screen, no matter how slight 
in amount, is distinctly detrimental to the picture. That 
is an absolute fact, which it seems to me any operator 
or manager ought to realize and understand, (c) House 
lights improperly arranged, or improperly shaded. This is 
another point concerning which some managers display an 
astonishing amount of crass ignorance or carelessness or 
both. I have actually gone into a theatre of considerable 
pretension, charging a good admission price, and found 
the white light from incandescent lamps shining directly on 
the screen, or found the white light shaded from the screen 
but glaring directly into the eyes of the audience. I do not 
care to take up the matter of house lighting here, but under 
the proper heading these things will be dealt with and such 
information as is available will be given on the subject of 
house lighting. 

Exhibitors and operators should be continually examining the 
screen, keeping a sharp lookout for stray light. They can only 
do this best when the projecting machine is not working no 
picture or projection light on the screen. The screen should 
then look the same all over, with absolutely no shadows. 

After having examined the screen, with the entrance doors 
closed, open them and see whether there is any difference, 
and whether, when the entrance and exit doors are swung 
open, shadows appear on the screen. If so, then the neces- 
sary steps should be taken to exclude the rays which cause 
these shadows. A few screens or double doors will very 
likely remedy the matter, remembering always that at matinee 
performances the shades on the windows must be absolutely 
light tight in order to get the best effect. This is best accom- 
plished by tight fitting wood or metal shutters, though two 
dark-colored shades, with their edges running in grooves not 
less than one inch deep, will serve. One will do fairly well, 
but is likely to develop pinholes; two are much better. 

Standing beside the screen, looking toward the auditorium, 
there should be no light visible to the eye at any point. If 
there is, then that light is reaching the screen and doing injury 
to the projection. 


Indirect lighting has been one of the best aids in elimina- 
ting stray light from incandescent lamps, but it is often improp- 
erly installed, and in many instances an indirect lighting fixture 
reflecting light against the ceiling and thence to the screen will 
cause more interfering light than any other possible installation. 
This by reason of the general practice of allowing too many 
and wrongly located fixtures to be illuminated during the show, 
and too much illumination per fixture. See "Lighting Audi- 

Tolerably dark wall decorations are a great aid in elimina- 
ting stray light; also they are more restful to the eye. Dark 
colors, such as green, give the picture greater contrast, and 
absorb interfering light. Daylight, however, is not only the most 
difficult of all stray light to exclude, but is also the hardest to 
absorb, and in hundreds of instances its presence robs the picture 
of beauty and detail. Dark decorations on the walls, however, 
can easily be carried to excess. There is room for good 
judgment and common sense here. It won't do to make the 
theatre gloomy; there is an extreme both ways. 

Distribution of Light. The screen not only reflects light 
to the eye located at one point, but the degree of roughness 
in its surface causes the distribution of light in all directions 
toward and throughout the auditorium of the theatre, so that 
the picture becomes visible from every point therein, and 
if the screen surface be such that distribution is even, then 
the picture will be as bright from one point as it will from 

In fact one of the important points of difference which ap- 
pears when comparing various screen surfaces is the difference 
in the direction these surfaces reflect the picture light. 

We may properly divide screen surfaces into four classes, 
viz: three classes of direct projection screens and one class 
of rear projection screens. 

First: A White Wall or Sheet. These surfaces were in 
general use for many years, and are still used to a large ex- 
tent, particularly in the smaller towns. The white sheet 
should be made of a reasonably good grade of bleached mus- 
lin, which may be had as wide as 108 inches. It must be 
stretched perfectly tight and be entirely free from sags and 
wrinkles. The plaster wall needs no description. It must, 
of course, be perfectly flat and finished with a white, hard 

When light strikes the white wall or sheet the peaks and 
depressions are so large, as compared with the wave length 
of light, that the light is reflected in very wide angles, and on 


this account a great proportion of the light is lost to the 
auditorium proper. The proof of this is that a white wall 
will appear brighter when one is up close to it or to the side 
of it than will any other screen, whereas it will appear darker 
in front and from the various points in the auditorium of the 
theatre. A metallized screen, or mirror screen placed against 
such a surface, will show a very great difference in brilliance 
of illumination. Therefore it is not possible to secure any 
very high percentage of efficiency with a white wall or 
cloth screen, as compared with the efficiency secured with 
semi-reflecting screen surfaces, because much of the light 
from the wall or sheet is not reflected to the viewing space 
of the auditorium, but in other directions. 

Second: Metallized Screens. Screen surfaces coated with 
various secret compounds containing more or less aluminum 
or other metallic substances are now quite popular. Metallic 
screens have for their base some kind of cloth, to which is 
applied a preparation containing a percentage of aluminum 
or bronze, though as a matter of fact in some of the modern 
"metal" surfaces but little actual metal is used. Screeni 
also have been made from tinfoil, attached to cloth and 
coated with celluloid. This formed the surface of the "Day 
arid Night" screen which was exploited for a considerable time. 

Bronzes and aluminum paints are difficult and impractical to 
apply in such manner as to secure perfect light diffusion, and 
the exhibitor should always buy such screens from reliable 
manufacturers who make a study of the preparation of such 
surfaces, and who usually supply stretching devices which allow 
of the screen being properly installed. 

Results from metallized surface screens depend upon the 
character of the surface. Evidence that the peaks and de- 
pressions on many metallic surface screens are smaller than 
on a white wall or sheet may be had by viewing the surface 
with a microscope, and when this is the fact, the effect is 
visible to the eye by viewing the screen from an angle and 
noticing the difference in the amount of light reflected from 
the side and the amount reflected straight back. You will 
usually find that away up to one side the "picture light" be- 
comes weaker, but as you go in front of the screen, at some 
distance away, it becomes very bright. 

For a wide house a special surface should be made which 
will distribute light at rather a wide angle, while for a nar- 
row house the highest efficiency is produced by a brilliant 
surface which concentrates the light to a narrow viewing 


The reflection of light by the screen is just as difficult and 
important an optical problem as is the projection of the pic- 
ture itself, and even as a lens which projects, a 9 by 12 picture 
at a certain distance does not and cannot project a 16 foot 
picture at the same distance, a screen which reflects evenly at 
a narrow angle cannot at the same time reflect evenly at a wide 

Third: Mirror Screens. This surface consists of a sheet of 
plateglass, the back of which is coated precisely the same as 
is an ordinary plateglass mirror. After the back has been 
silvered, its face is ground to a dull finish, which is made 
rough or smooth, according to the conditions under which it 
is to work. The light is caught on the ground face, goes 
through, strikes the silver at the rear surface, and is reflected 
back to the rough finish. This has the effect of producing 
very high efficiency, or, in other words, a very high brilliancy 
for a given amount of projected light. The mirror screen is 
packed and shipped in a permanent frame, and is all ready 
to install when received. 

A picture projected upon a plain lookingglass would not 
be visible to the eye because the polished surface will reflect 
to the eye rays from all points so located that a line drawn half 
way between the eye and the object and at right angles to 
another line drawn from the eye to the object will strike the 
mirror. Therefore since the picture comes from the lens, 
instead of an image of the picture you merely get a reflec- 
tion of the bright spot light at the lens and an image of the 
auditorium, as a whole. In order that the picture become 
visible on the screen, it is necessary that diffuse reflection be 
substituted for direct reflection, or, in other words, that the 
picture light be "broken up," and this is accomplished by 
grinding the surface of the glass to a dull finish. 

The manufacturer claims that the mirror screen produces 
two ideal results, viz: first, the surface may, within reason- 
able limits, be made with either large or small peaks and 
depressions, so that for a wide house the light is distributed 
at a wide angle, whereas with a narrow auditorium it is con- 
centrated to a narrow viewing angle. Second, the surface is 
perfectly dull, without shine, and as a consequence only dif- 
fuse reflection is present, the same as on a dull, white wall, 
therefore a clear-cut, clean picture results. 

To sum up matters pertaining to the mirror screen, it may 
be said that if the screen be properly selected with reference 
to local conditions high-class results should be obtained by 
its use. It is costly, but is in the nature of a permanent in- 


vestment, since, barring highly improbable accident of break- 
age, it :'s to all intents and purposes indestructible, and once 
installed should require no attention whatever for many 
years, except an occasional cleaning, which is not at all diffi- 
cult and consumes but little time. The mirror screen is 
peculiarly adapted for use in very long auditoriums because of 
the fact that a person with average eyesight will see a perfect 
picture even when several hundred feet away from a mirror 

Transparent Screens. The transparent screen must be 
made of translucent material, so that the machine can be 
placed at its rear or back side and the picture be viewed by 
the audience in the auditorium through the screen. The image 
appears on both sides of the curtain, but appears "backward" 
to the operator. 

The film is placed in the machine with the emulsion side to- 
zvard the screen, instead of toward the light as in ordinary pro- 

It is possible to use ordinary cheese cloth or thin muslin 
for this purpose, but if this is done the machine must of 
necessity be set lower than the screen and "shoot upward," 
nor can such a screen be used at all where there is a gallery 
in the theatre. The reason for this is that if any portion of 
the audience sit in suc'h position that the eyes will be in 
line with any portion of the picture and the lens, they will 
see the bright lens spot through the screen. 

The translucent screen, however, breaks up this bright 
spot and renders it invisible. If a cloth screen be used tbe 
result will be greatly improved if it is kept wet with water. 
The best screen for rear projection is ground glass, which 
lends itself particularly well to rear projection, because there 
is but slight loss of light, and furthermore the surface may 
be ground, fine or coarse as desired, in order to distribute at 
wide or narrow angles for a wide or narrow house. A fairly 
satisfactory transparent screen is made from tracing cloth, 
the worst difficulty being that it cannot be obtained suffi- 
ciently wide, and must of necessity contain a seam, which 
will show more or less in the picture in spite of anything 
one can do. 

Rear projection is, however, not very much used. It pre- 
sents advantages where conditions are such that it can be 
used properly, but in four cases out of five where it is at- 
tempted there is too short a throw to get the best results. 
In fact it is usually employed as a makeshift. Properly 
used, that is to say where the distance from machine to 


screen will be such that an objective lens of not less than 4 
inch E. F. will be required, rear projection on a glass or 
other high-class translucent screen comes pretty near being 
ideal, since the operating room, with its noise, heat and fire 
risk, is located entirely away from the audience, and pre- 
sumably outside the theatre. 

If this be done, and the operating room be located in a 
separate structure, it will be necessary to locate the screen 
in an opening in the theatre wall, and this opening must be 
protected by a sheet of plate glass, outside the screen, with 
the space between it and the screen closed in tightly to form 
a dead air space. Otherwise there is apt to be trouble with 
frost in winter. It is also necessary to protect the light ray 
from rain and snow if it shoots across an open air space. 
Rear projection is seldom employed under these conditions, 

The question is often asked of the writer: Can we locate 
a transparent screen at the proscenium line, set the projec- 
tor at the rear of the stage and get a good picture? The 
answer is no! It is never advisable to attempt the projection 
of a picture of a size suitable for theatre work with less than 
50 feet from lens to screen, and 40 feet may be considered 
as an absolute minimum, understanding, however, that really 
high-class results cannot be had at 40 feet unless the picture 
be much smaller than is suitable for a theatre. Another 
objection to this plan is that it brings the front seats too 
close to the screen. 

Eye Strain. About thirty-five people in every hundred 
avoid the picture theatre either on account of eye strain or be- 
cause they fear injury to their eyes. Eye strain in moving 
picture theatres may, broadly speaking, be attributel to four 

First (and greatest) : Flicker and Unsteady Light. In this 
case the retina of the eye expands and contracts so rapidly, 
in attempting to adapt itself to the changing light intensity 
of the screen,) that the muscles of accommodation are sub- 
jected to terrific strain. This sort of eye strain is so obvious 
and so well understood that comment seems almost unneces- 
sary. As light becomes stronger or weaker the pupil of the 
eye expands or contracts. It is nature's way of regulating 
the amount of light reaching the retina of the eye. When 
this change occurs continuously and rapidly, however, the 
strain is highly injurious. In this connection it may be said 
that in nine cases out of ten where there is an objectionable 


flicker it can be eliminated, or at least very greatly reduced, 
if the operator understands his business, and is able to match 
his shutter-setting and width of blades to local conditions. 
The screen itself, as such, never produces flicker, but where a 
screen of comparatively low efficiency is used and a screen of 
the same area but of higher efficiency is installed using the 
same amperage, this tendency to flicker will be increased by rea- 
son of the added brilliancy of the light. The period of dark- 
ness remains the same, but the light is much more brilliant, 
hence there is increased contrast. If the brilliancy of the 
picture were reduced to its former value by cutting down 
the amperage, it would be found that the flicker would be 
neither greater nor less than it was before. 

It may be stated as a fact, that, in this day of improved pro- 
jection apparatus, a pronounced flicker is inexcusable. Either 
there is something wrong with the knowledge of the operator, 
with the condition the projector is working under, or the speed 
of projection is too slow. 

Second: Eye strain may be and is caused by lack of defi- 
nition in the picture, which, in turn, may be due to a dirty 
lens, a badly matched lens system, or to a poor objective, 
to poor condenser, or to fault inherent in the film itself. On 
this account it is of very great importance that lenses of good 
quality be used, that they be kept perfectly clean, and that 
the operator have his picture in absolute focus at all times. 
It is also important that manufacturers send out no film 
which, through inherent fault, cannot be projected with per- 
fect sharpness. See Page 152. 

Third: Eye strain will be caused by poorly illuminated, in- 
distinct or jumping pictures. An intensely absorbing picture 
story will cause the audience to strain every effort to catch 
every phase, every word, every expression of the face and 
action of the artist on the screen. Sometimes an apt expres- 
sion, though slight in detail, will change the entire meaning 
of what the actor seeks to portray. We try to see, and, by 
reason of dimness or "jumpiness" of this film, strain our eyes 
iti the effort. 

We read the picture story just as zve do a book, and if we 
attempt to read a book in poor light or when it is shaking or 
moving, the result is strain upon the eye, which is entirely avoid- 
able by simply moving into a better light and holding the book 
still. This is only a matter of plain common sense, and needs 
no argument in its support. 

Precisely the same thing applies in projection, only instead of 
"moving into better light" we get the same effect by project- 


ing more light to the screen, and instead of "holding the 
book still" we prevent the film from jumping. 

Fourth: Eye strain is often caused by the use of too large 
a screen, with a portion of the seats placed too near it. For 
example: we breathe by unconscious motion, exactly as the 
eyt automatically changes its position to focus itself upon the 
exact point we wish to see, without any special mental effort 
on our part. If we sit near a large screen* the eye will 
naturally try to follow the film story, and in so doing will 
move all over the surface of the screen, moving continuously 
and very rapidly. Just imagine the gymnastics the eye is 
called upon to perform under such conditions. I venture the 
assertion that a glass eye would not stand up very long under 
that sort of treatment, much less the delicate organism of the 
human eye. 

Flat Surfaces Location. It goes without saying that what- 
ever the surface of the screen be composed of it should be 
perfectly true and flat, without wrinkles, bumps or uneven 
places; also it should be set as nearly as possible with its 
center level with and in line sidewise with the lens. This 
latter condition is not always practical of accomplishment, nor 
is an angle of projection which does not exceed 25 per cent 
(3 inches to the foot or IS inches in 60) very seriously 
objectionable, though a side throw is highly so. 

The practice of some large houses in placing the projection 
machine at the top of a very high gallery and angling down 
at about 45 degrees toward the screen is a very, very bad 
one. It causes keystone effect, and, even allowing that this 
may be eliminated by filling in the machine aperture, the 
distortion of the picture is still there and is not pleasing to 
the eye. Many attempt to compensate for this by leaning 
the top of the screen back a little, but if it is leaned much 
more than twelve inches from the perpendicular the appear- 
ance is unsatisfactory, especially from the main floor. Locat- 
ing the operating room thus wrongly is usually due directly 
to the fact that the exhibitor refuses to sacrifice seating 
space on the main floor in a lower balcony. He prefers the 
permanent injury of his projection to the sacrifice of a few 
seats. The operating room could usually, by proper plan- 
ning, be placed in a lower balcony or even on the main floor. 
The gain in excellence of projection would far more than 
compensate for the few seats lost. Its exterior walls could 
easily be decorated in such manner that its appearance would 
not be at all objectionable, and, in general, as I have said, the 
results would be far more satisfactory. 


Tinted Screen Surfaces. At this writing (last half of 1915) 
it is very much the fashion for screen manufacturers to tint 
the surface of their screens. Some manufacturers put out 
several surfaces, such as plain metallic, flesh tint, faint 
yellow, etc. The author is not in accord with this practice. 
While freely granting that tinting the surface of the screen 
may and probably will have the effect of softening the tone 
of the picture, still he does not believe there is anything so 
beautiful *as the plain black and white projection, with a 
pure white light and as nearly as possible a pure white 
screen surface. The only tinting he believes in is the ad- 
dition of a little blue to the white when mixing a screen 
paint or calcimine, this being for the purpose of rendering 
the white paint still more white, just as the laundryman adds 
bluing to the rinsing water in order to make the clothes 
more white. You will therefore see that this sort of tinting 
simply follows out the author's idea of making the screen 
as white as it is possible to get it. 

Let it be noted, however, that I am willing to give due 
credit to the ideas and opinions of others, and in this matter 
simply express my own individual opinion. 

Outlining the Picture. It is wonderful what a difference 
in effect is produced by giving the picture a proper border 
or outline. There is nothing so effective for this as a soft, 
velvety black, such as is produced by ordinary dry lamp- 
black, mixed with one-third linseed oil and two-thirds tur- 
pentine. This form of outline is shown in Fig. 69. In 
order to outline the picture thus proceed as follows: Get the 
light from both machines registered on the screen exactly 
where you want it, and then with the plain white light pro- 
jected to the screen draw a pencil line about 2 inches inside 
the light all around, making the corners round, just as the 
light is on the screen. Now shut off the light and paint 
all the screen on the outside of the line black. This sort of 
outline adds very greatly to the brilliancy of the picture. 

Where the black border is used there is not only less 
distraction for the eye, but the effect of added light brill- 
iancy is 'had without its actuality. This is of very distinct 
advantage, since every increase in actual light brilliancy 
has a tendency, to accentuate any tendency there may be to 
flicker. With very brilliant light and normal speed of the 
projector, even the more modern three-wing shutters do not 
entirely get rid of the flicker. By the use of a black outline 
the picture appears much more brilliant, owing to contrast, 



whereas it actually remains exactly as it was, and thus the 
effect of added brilliancy is attained without flicker increase. 

The black border cannot be used, however, where a stere- 
opticon picture having a height greater than the height of 
the moving picture is to be projected on the same screen; 
also it must be remembered that the paint for the border must 
be dull black without any gloss at all. 

The reason for allowing the picture to lap over on the 
black is that it greatly minimizes the effect of any movement 

Figure 69. 

of the picture on the screen; also it hides any vibration 
there may be in the machine aperture itself. Such vibration 
should not be present, but sometimes, owing to a poorly 
constructed operating room floor, it is. 

Where the screen is set back on the stage the better plan 
is to outline the screen with black, as above set forth, and 
then from its outer edge stretch black cloth having a per- 
fectly dull finish (velvet is best, though rather expensive), 
to the inside edge of the proscenium wall on both sides and 
above, thus forming a sort of funnel. If rightly done, the 
cloth preferably being in pleats or folds it is very effective, 


and sets off the picture splendidly. The stage floor in front 
of the screen should also be painted dull black. 

Black may be objected to as too somber and there is foun- 
dation for this objection. Black, however, is best from the 
projectional point of view, but other dark colors may be sub- 
stituted, such as green, violet, lavender or old gold, and instead 
of forming a funnel a more or less elaborate arrangement or 
stage setting may be preferred. In fact the possible combina- 
tions are limitless, but stick to dark colors, with at least a two 
foot band of dead black next the picture. 

Locating the Screen in Front of the House, that is to say, 
at the end where the audience enters, ivith the operating room 
at the rear end of the auditorium, is bad practice, and unless 
required by local law should not for one moment be considered. 
The effect is bad in every zvay. 

Those entering and going out must perforce pass beside 
the screen, which has the effect of constantly distracting at- 
tention from the picture. The idea which has caused the 
lawmakers of some localities to enact ordinances requiring 
this sort of screen location is based on the view that in case 
of fire in the operating room the audience will not be obliged 
to pass near it and therefore will not become panic-stricken. 
That argument sounds very nice; also it looks well in print. The 
only fault that could possibly be found with it is that it 
doesn't work out in practice. If an operating room fire occurs 
with the operating room near the entrance of the theatre 
the audience hestitates to some extent to pass it, and is, 
to just that extent, deterred from making a rush, but if the 
operating room is located at the other end and a fire occurs, 
good night! Somebody yells fire: There is nothing in the 
world to stop them. They make one grand rush and pile 
up in a heap at the entrance. Result: many injured, and prob- 
ably some killed. There is no earthly necessity for such 
laws, anyway. If the operating room be rightly constructed, 
equipped with a proper vent flue and has a properly ar- 
ranged shutter system, you can burn several reels of film 
therein and the audience will never know there is a fire. 
// our distinguished lawmakers would pay more attention to the 
proper arrangement of the vent flue and fire shutters of the 
operating room t and not so much to foolish ideas of this sort, 
it would be much better for all concerned. 

Where the screen is located on the stage and the house 
is a short one, say less than 75 feet in depth, it is much 
better to set the screen back as far as you can get it without 


seriously interfering with the view from extreme side seats. 
Those in the rear will still be close enough to have an ideal 
view, while those in the front rows and at the side of the 
auditorium will have a vastly improved view over what it 
would be if the screen was at the proscenium line. 

Where Vaudeville Is Used. In many theatres where a 
mixed performance is given it is necessary that the screen be 
placed near the curtain line, in order that the stage may be 
set while the picture is being run. The majority of houses 
of this kind use a plain cloth drop, usually outlined in black. 
Such a screen will sway with every breeze, or will move 
when touched by stage hands working at its rear. A much 
better plan would be to frame this drop substantially, though 
lightly, and back it with light lumber. At either side 
grooves can be arranged so that the screen will always set 
precisely in the same spot when lowered, and will at all 
times be perfectly flat. All this is entirely practical, and 
should be carried out, though it, of course, applies only to 
houses having a fly loft. Such a screen would be tolerably 
heavy, but could easily be counterweighted to handle with 
perfect ease. 

Height Above the Floor. The height of the screen above 
the floor must be governed by circumstances, but where 
there is a stage I believe the general effect is best if the 
bottom of the picture be located quite near the stage floor. 
True, there is a distinct advantage in locating the picture 
high up on the wall, since it does away with the obstruction 
to the view caused by persons seated in front. Such a 
location, however, also has serious disadvantages, which, 
in my opinion, far more than outweigh the gain. The 
disadvantage is that the picture is not shown in the normal 
level position in which we are accustomed to look at such 
scenes in real life. It has, I think, a decided tendency to 
emphasize in our mind the fact that we are looking at. a 
picture, and not a real performance. Everything considered, 
I believe that locating the bottom of the picture at as nearly 
as practical six feet above the auditorium will usually be 

Size of Picture. Much has been said, and many arguments 
have been advanced for and against the large and the small 
picture. The question is just as strongly debated today as 
it ever was. Personally, I do not believe there is or ever will 
be any set rule as to the picture size which can always be 
followed to advantage. The photograph, as projected through 


the machine aperture, has very considerably less than one 
square inch of area. We therefore see that the magnifica- 
tion is, in any event, enormous, and we must remember that 
Every defect in photography, every movement of the film, and 
every scratch mark and jump is magnified as the size of the 
picture is increased. Also we must remember that as the size 
of the picture is increased the light strength must also be rapidly 
increased, if the brilliancy of picture is to remain- as it was. 

You have a light strength produced by 30 amperes D. C., 
let us assume. You are projecting a 12 foot picture. This 
means that the light is distributed over 108 square feet of 
area. Suppose you increase the size to 16 feet. You now 
have 192 square feet of surface almost double that of the 
12 foot picture; hence the curtain brilliancy obtained from 
your light is decreased by almost one half. You must in- 
crease the amperage very greatly to secure illumination 
equal to that of the 12 foot picture. You will therefore see 
that a large picture is costly, in current consumption or in 
sacrifice of brilliancy. See Page 165. A 12 foot picture is con- 
sidered as being "life size." A picture of this size is, to one of 
normal vision, perfectly distinct in all its details 75 or even 
100 feet away, or much further if it be a mirror screen. It 
is seldom there is any real reason for projecting a larger 
picture, so far as ability of the audience to see the details 
of the picture b concerned. It must, however, be granted 
that in a large house a 12 foot picture seems somewhat out 
of proportion, especially if the screen be located on a large 

One other very important factor enters, viz: ability of 
those in the rear seats clearly to see the faces of the actors, 
this by reason of the fact that in the silent drama very much 
often depends upon facial expression. The glance of an eye 
or some movement of the features may change the whole 

However, again no rule can be given which will apply to 
all cases. With a high grade lens and a perfectly sharp, 
brilliant picture these things are clearly discernible under 
conditions which would render them almost invisible with 
weak light or poor, "fuzzy" definition. 

The size may be increased very greatly, but it is always 
at the expense before mentioned. The possible limit depends 
on local conditions, and how much you are willing to expend 
for current and good lenses; also mirror screens do not ex- 
ceed 13^2 by \8 l /2 feet in size. For a throw of 50 feet, fifteen 
feet ought to be the limit, since with a wider picture optical 


difficulties are encountered. A very short focal length pro- 
jection lens is required to project a wide picture on a short 
throw, and such lenses seldom give sharp definition. With 
a throw of 75 feet, an 18-foot picture is as large as it is 
well to attempt. At 100 feet almost any size you can illumi- 
nate may be projected. To put the matter concisely, I do 
not advise the use of a projection lens of less than 4 inch 
equivalent focus. This matter will, however, be treated 
more exhaustively under "Lenses." Mr. Frank Rembusch, 
who has made a study of such matters, says : 

"If a screen is too large, an elongation of faces and figures 
results, especially on a short throw, where the house is short. 
If the screen is too small the results also are not satisfactory. 
To some extent, of course, it is a matter of taste, but after 
consulting the best authorities, together with inquiries among 
lens manufacturers as to what can be done, I have arrived 
at the following opinion: A house 25 feet wide and 75 feet 
long should have a screen about 9 feet by 12 feet, and the 
longer or wider house in this proportion. For instance, a 
house 40 feet wide and 100 feet long should have about a 
12 by 16 screen; a house 25 feet wide and 125 feet long should 
have about an 11.6 by 15.4 screen. No screen should be 
larger than 12 by 16, except where the first row of seats in 
front can be located at least 30 feet distant therefrom, 
and the throw is not less than 125 feet. Here is your limit. 

"A larger screen will cause eye strain up close, and with a 
shorter throw will cause elongation of the faces and figures, and 
a distortion of the pictures." 

Certainly friend Rembusch is rather extreme in his state- 
ment that it is not well to attempt the projection of a pic- 
ture larger than 16 feet at less than 125 feet. I am of the 
opinion that a practically perfect 18-foot picture may be 
projected at 100 feet (5% inch E. F. lens), or even a little 
less. His other statements I agree with, however. 

Coatings. Many managers, particularly in the smaller 
towns, and, to some extent in the small theatres of the 
larger cities, prefer to use a home-made screen, which they 
construct of cloth, plaster, and occasionally of metal. I have 
already set forth the relative points of excellence as between 
the cloth, plaster, metallized and mirror surfaces, to which 
I will add the further remark that cloth, or plaster properly 
coated, gives as artistic a projection as it is possible to 
produce on any surface. The difference between it and the 
more costly screen is found in the fact that with the latter 


surfaces much greater brilliancy is had for a given amperage 
than is possible with either cloth or plaster. 

The traveling exhibitor, as a general proposition, uses an 
uncoated cloth "sheet," but where cloth is used in a perma- 
nent location it should be stretched very tightly on some sort 
of frame, coated with a size made by dissolving a good 
grade of glue in warm water. I do not remember the exact 
amount, but, at a guess, would say about one pound of good 
glue to an ordinary pailfull of water. When the sizing is 
thoroughly dry the screen may receive its final coating, 
which may be (a) white lead or zinc ground in oil (to be had 
at any paint store), mixed about in the proportion of one- 
fourth boiled linseed oil and three-fourths turpentine, to 
which has been added just a little ultramarine or prussian 
blue not much, but just enough to give the paint a rather 
pronounced bluish tint while in the pot. It will look per- 
fectly white on the screen, (b) One of the patent white 
calcimines, such as muralite, alabastine, etc., also to be had 
at any paint store. No matter whether paint or calcimine 
is used give the curtain two or three coats, rather than one 
heavy one, and be sure there are no brushmarks when the 
job is finished. After the final coat has dried, outline the 
screen in black, as already directed. See Page 178. 

Where a plaster screen is used I would recommend that 
it be of cement finish, rather than ordinary hard coat, be- 
cause the cement may be calcimined and the calcimine 
washed off and renewed many times without in any way 
affecting the underlying surface. The plaster or cement 
should be coated with one of the patent calcimines as before 
mentioned even though the surface be plaster. The cal- 
cimine will give a considerable better projection surface 
than will the plaster itself. 

Caution. Do not imagine you can coat a cloth or plaster 
screen with calcimine or paint and use it indefinitely without 
doing anything more to it. 

I would very strongly recommend that where a plaster 
calcimine coated screen is used, it be washed off and re- 
coated at least once every sixty days. It may look clean and 
bright, but you may take it from me, it is not. The wall paper 
or calcimine on the ceiling of your home may look perfectly 
clean, but rub your damp finger on it and see if it is; per- 
haps the result will astonish you. The same thing applies to 
the screen. Calcimine is cheap. My advice is to USE IT FRE- 


Paint may be washed, if it is carefully done, but it is not 
the same as new. I much prefer calcimine to paint on a 
plaster surface, but if paint is used, the plaster should be first 
thoroughly sized. 

Caution. Don't attempt to make home-made metal surface 
screens by applying aluminum to cloth or plaster. There is 
about one chance in a hundred that you will get anything even 
approaching satisfactory results. Calcimine or paint is much 
better than ninety-nine out of every hundred home-made alu- 
minum screens. 


The Mirror Screen. The salient points concerning the 
niirror surface made by the Mirror Screen Company, Shelby- 
ville, Ind., have already been set forth. The screen is a 
high class article, and has many enthusiastic suporters among 
exhibitors. It gives a very brilliant picture per ampere of 
current used. It is expensive in first cost, but will last 
practically forever. The surface must be very carefully 
selected with reference to the conditions under which it is to 
work. For the long, narrow house, get a smooth finish, but 
for a wide house get it just as rough as possible. It comes 
all packed in a box, ready for installation. Its surface can be 
washed perfectly in a few moments. The silver backing is 
guaranteed against deterioration. 

There are nine different mirror screen surfaces, designed 
for use in theatres of varying dimensions. Mirror screens 
have been in use in theatres for several years. Therefore 
they have been thoroughly tested as to their efficiency, and, 
as already stated, when properly selected with reference 
to local conditions results from them are excellent. They 
may be had in the following widths: 8 feet, 8 feet 8 inches, 
9 feet 4 inches, 10 feet 8 inches, 11 feet 4 inches, 12 feet, 
12 feet 8 inches, 13 feet 4 inches, 14 feet, 14 feet 8 inches, 
15 feet 4 inches, 16 feet, 16 feet 8 inches, 17 feet, 17 feet 4 
inches, 17 feet 8 inches, and 18 feet. The last four widths 
require slot cars for their shipment. They are made as small 
as required, but 8 feet is about the minimum used in theatri- 
cal work. 

When exhibitors erect a theatre and contemplate installing 
a mirror screen they should remember that the screen must 
be brought in before the walls are closed in, as it is all in 
one piece. The 8-foot screen is 6 feet high, with probably 
a foot added to that for packing, and in an old house it may 


be necessary to cut a slot in the wall, over a door or else- 
where, to get a mirror screen in. 

The prices range from $135 for an 8-foot screen to $1,000 
for the 18 footer. 

The same company also manufactures metallic surface 
screens of various kinds, made of seamless cloth, and the 
surface is guaranteed against deterioration for a period of 
five years. 

Simpson Solar Screen. One of the oldest metallic surface 
screen surfaces on the market is the Simpson Solar Screen, 
manufactured by the Simpson Solar Screen Company, New 
York City. This surface is of pure, carefully selected alumi- 
num. Each screen is hand-made, and the surface thus pro- 
duced gives sharp contrast as between the whites and blacks; 
also it gives great brilliancy to the whites. 

The screen is made in one piece up to twelve feet in width. 
The author can vouch for the excellence in results from this 
surface. It is guaranteed against peeling, tarnishing or other 
defect for a period of five years, and its manufacturers assure 
me that the guarantee will be made good. 

The surface is slightly, though not heavily matte. The 
reflection is entirely diffuse, there being no direct reflection, 
therefore no haze. 

The Mirroroid Screen. The J. H. Center Company, New- 
burgh, N. Y., manufactures the mirroroid screen, which is a 
product familiar to exhibitors pretty much all over the coun- 
try. Mirroroid screens have a matte surface. The com- 
parative matte of the various mirroroid surfaces is shown 
in Fig. 70, which is a full size photograp'h of samples of 
the material. In the opinion of the writer the rough surfaces 
are best adapted for use in wide houses, and it is his opinion 
that, w.hereas the matte or visible roughness of the surface 
has little or nothing to do with the actual diffusion of light, 
still it has a very beneficial effect in enabling the spectator 
who views the picture at a side angle to get a good detail 
of the picture. There is a distinct difference in the effect 
produced by the visible roughness of the matte surface, 
and in the effect produced by the invisible peaks and de- 
pressions before described. One produces light diffusion and 
the other gives detail to the picture when viewed from an 
angle, or, at least, that is my opinion. Each is of impor- 
tance to perfect projection. 

Mirroroid screens have given very general satisfaction, 
and can be recommended to the consideration of exhibitors 
who are looking for a good article. They come in a variety 



of tints, such as plain "metallic surface," "silver white," 
"flesh" tint, etc., and the surfaces are guaranteed against 
deterioration for a period of five years. They are seamless 
up to about 11 feet wide and above that a special treatment 
tends to render the seam invisible. 

Figure 70. 

The Minusa. The Minusa Cine Products Company, St. 
Louis, is putting out various types of metallic surfaces, its 
specialty being the Minusa Gold Fibre Screen. This com- 
pany produces screens, some of which have very rough sur- 
faces, as shown in Fig. 71, which is a full size photograph 
of samples submitted by the Minusa concern. These screens 



are fully guaranteed for a period of five years against de- 
fective workmanship, discoloration, etc. 

The Radium Gold Fibre Screen is one of the oldest and 
most widely advertised of the many so-called "patent" pro- 
jection surfaces. Radium Gold Fibre is a metallized screen 

Figure 71. 

and is frankly sold as such, with all arguments both for and 
against the metallized projection surface kept constantly in 
mind by those who are marketing it. A high grade gold 
bronze is the basic ingredient of the surface coating, and 
the arguments for and against the use of yellow in projection 
surfaces are well known. Unquestionably the radium gold is 


an excellent surface for those who favor a yellow-tinted sur- 
face. It is made by Radium Gold Fibre Screen, Inc., 220 
West Forty-second Street, New York. 

Stippled Surface. The following is a scheme for which it 
seems H. E. Hammond, manager of the Crescent Theatre, 
Erie, Pa., is responsible. It is a new one and I only give it 
for what it is worth, with the remark that it looks very 
good. It has been reported on favorably by the operator 
who installed the projection plant in the Crescent. 

Mix dry zinc (to be procured from any paint store) with 
water, making it as thick as can be spread with a paint brush. 
Then paint the plaster wall with the mixture, and follow up 
with a wide, flat brush, pouncing the wet surface with the 
ends of the bristles of the brush. Let it dry thoroughly. 
Apply a second coat and pounce in the same manner; let this 
dry and apply a third coat, again pouncing with the brush. 
The result is a flat surface, covered with little round craters, 
or depressions. 

This ought to make a very white surface, and, moreover, 
the effect should be good. It is said that the picture shows 
up much better on a wide view where this surface is used. 

Chalk Surface. Still another surface has been favorably 
reported. It has in its favor the fact that it may be easily 
and cheaply tried out. It consists of rubbing any suitable 
surface thoroughly with ordinary white chalk, school crayon 
broken into pieces two inches long and used flatwise will do, 
but chalk such as mechanics use for chalk lines (obtainable 
at hardware stores) is much the best. It is said, and it 
sounds reasonable, that a picture projected on this surface 
stands out with great brilliance. You must, of course, get 
the chalk rubbed on evenly. 

Fire-Proofing. Any fabric may be fire-proofed by thor- 
oughly saturating it with ammonia phosphate mixed in the 
proportion of one pound to one gallon of water. In the 
case of a cotton screen I would stretch it tightly on a frame, 
dissolve the phosphate in water and saturate the fabric 
thoroughly by using a new, cheap paint brush. Let it dry 
and, while it will char, it will not and cannot be made to 
blaze. A lighted match would char the fabric where it came 
in actual contact with it, but that would be all there would 
be to it just a hole in the cloth. Phosphate of ammonia 
may be had of retail druggists at about 75 cents a pound; 
wholesale it is much cheaper. There is nothing in phosphate 
of ammonia that will injure the fabric. Wood soaked in 



Figure 72. 

this solution is made thoroughly fire-proof in the sense that 
it cannot be made to blaze. 

Stretching the Screen. The Mirror Screen Company, which 
also manufactures metallic surface screens, suggests the use 

of a frame known as 

the "artist frame" for 

mounting moving pic- 
ture metallic surface 
screens or cloth screens. 
Some years ago the 
mounting of a screen 
was of little importance. 
A cloth screen was 
mostly used, and due 
to low reflective power, 
uneveness or wrinkles 
therein were scarcely 
visible; moreover a 
thin cloth could be 
stretched taut on almost 
any kind of a frame. Of late, however, the wide use of metallic 
surface screens, many of which are on a heavy canvas, makes 
it necessary though very difficult to stretch them tightly, 
since with a semi-reflective surface every wrinkle or uneven 
place will show badly. 
There is nothing bet- 
ter adapted for this pur- 
pose than what is 
known as the "artist 
frame." It is much 
superior to any home- 
made arrangement, and 
may be purchased from 
almost any screen manu- 
facturer for less than it 
would cost an exhibitor 
to make it. It is simple, 
and I believe quite satis- 
factory. It may be Figure 73. 
shipped K. D., and the 

process of putting it together is one which can be readily per- 
formed by any man of ordinary intelligence. Begin to put the 
frame together by laying it bottomside up, on a floor or other 
flat surface. After the corners are bolted together see that 



every corner and the whole frame is exactly square. This may be 
tested by measuring diagonal corners. If the distance from 
diagonally opposite corners is equal the screen is square. Now 
put on the back braces and then turn the frame over or set up- 
right in place. The various steps in the process are shown, in 
their order, in Fig. 74. 

Putting on Cloth. The cloth should be rolled up so that 
the edge that goes to the top unrolls first. It may be put on 
either with the frame standing up or laying down. Standing 
the frame upright is the best plan, however, because the 
cloth will partly stretch by its own 
weight, and the whole job will be 
more easily and better done. A 
good start insures success. Lay 
the roll of cloth on a level floor; 
unroll a foot or two, and stretch 
a chalk line to determine whether 
or not its edge is perfectly 
straight. Trim it, if necessary, to 
fit the chalkline. Now make a 
chalkline across near the extreme 
edge of the top of the frame, on 
the front side, where the, cloth 
is to be tacked. The straight top 
edge of the cloth and the line on 
frame are placed together, and 
the cloth is tacked fast, thus in- 
suring a good, straight start. 

Tacking on Cloth. Place the 
tacks about two inches apart. A 
thin tack with a large, flat head 
is the best. If the frame is 
placed upright a piece of cheese- 
cloth should be looped and nailed 
to the frame on each end, to hold 
the roll of cloth in position while the top edge is tacked in place. 
Start at the center of the top, and tack both ways along the chalk 
line, until within about three or four feet of the corner. A 
single tack will hold each corner in position until you are 
ready to tack corners. Now unroll cloth slowly and carefully, 
keeping it stretched at all times. Stretch and tack the bot- 
tom of screen, beginning at center and working again to 
within three or four feet of each corner. Now tack one side 
at center to within a short distance of corner, and then tack 

Figure 74. 


and stretch the cloth on the other side, after which finish up 
the corners. 

In tacking any cloth screen always begin at centers of each 
side and finish corners last. 

If the work is done carefully the surfaces will be almost 
entirely free from wrinkles, and where a light cloth is used 
and well stretched by hand a very even surface is possible 
on a common hand-made frame. The artist frame we arc 
describing is provided with finishing strips which are nailed 
to cover up the tacks and raw edge of the cloth, and this 
helps the appearance very much. Beveled stretcher strips are 
then pushed down between the cloth and frame from the 
back, giving the appearance of a bevel around the edge on the 
face side. This gives a handsome, finished appearance to 
the screen generally. 

In most cases the cloth is free from wrinkles when the 
stretcher strips are put in position, but to provide for fur- 
ther stretching lag bolts are placed in the frame which, when 
screwed in, push out the stretcher strips still farther, so 
that the screen can be made as tight as a drumhead. The 
artist frame is always good property, as it can be used again 
for new cloth. Those exhibitors who use metallized screens 
should renew them at least every two years. Many metallic 
screen surfaces lose their brilliancy in even less time, and 
often those of inferior quality will become dull within a few 
months. Fig. 72 shows front of finished screen. 


The film is a strip of celluloid \Y% inches wide, by from S l / 2 to 
6 thousandths of an inch thick. In the process of making 
the celluloid is originally in strips about 2 feet wide by 250 to 
300 feet in length. These wide strips are passed through a 
machine which spreads upon one side a coating (negative or 
positive, according to the use to which the stock being treated 
is to be put) of photographic emulsion, approximately one- 
thousandth of an inch in thickness, this being a part of the 
thickness of the film as above given. 

After having received its emulsion coating the film is run 
through another machine, which splits it into ribbons \Y% inches 
wide, and these ribbons become the film stock which is pur- 
chased by the photoplay producer. 

The negative stock is first perforated and then, as needed, 
is placed in a camera having an intermittent movement, re- 
volving shutter and lens very similar in action to those of the 
projection machine (except that the mechanism is inclosed in 


a light-tight box or casing), and each three-quarters of an 
inch of its length is successively exposed to light, and what 
is essentially a "snap shot" photograph impressed thereon at the 
rate of sixteen per second (that is to say sixteen per second 
is supposed to be the rate, but in practice camera speed varies 
considerably). After exposure the negative is developed, fixed 
and dried much the same as any ordinary kodak negative 
would be the actual mechanical methods differ from the kodak 
film, of course, as the negative film will be more than 200 feet 
long, but the chemical action is precisely the same. The negative 
is then run through a projection machine so that the director 
may check up his work, make the scene over again, if necessary, 
or <cut out any undesirable portions. When the negative is 
finally in acceptable form, it is placed in a printing machine in 
contact with a strip of positive film (positive and negative 
film are exactly the same, except that a different grade 
or kind of photographic emulsion is used), and by means of an- 
other intermittent movement and revolving shutter, but without 
a lens this time, is exposed to artificial light of known power, 
each picture being exposed for the small fraction of a second. 
The positive film is then developed, fixed and dried, after which 
it is sent to the assembling room, where the various scenes con- 
stituting a complete photoplay are arranged in sequence, joined 
together, the titles and sub-titles put in, and it becomes the 
"reel of film" with which we are all so familiar. 

These, very briefly and crudely, are the processes a film 
goes through in the course of its making. 

The perforating is usually done by the producer, though 
perforated stock may be bought from the film stock maker. 
There are 64 perforations to the foot on either side, or four 
to the picture. Film perforation is one of the most vexing 
problems with which the producer is confronted. Unless it 
be done with absolute accuracy there will be unsteadiness, 
and if the negative be unsteady in the camera, and the 
positive be unsteady in the projection machine, the effect is 
to magnify the slightest inaccuracy in workmanship and 
produce a very unsteady picture on the screen. Then, too, 
even with absolute mechanical accuracy in the perforating 
room, carelessness in the drying room may cause trouble, or 
inequality in thickness of film stock may cause uneven shrink- 
age, and again there is unsteadiness in the final result on the 
screen. It will thus be seen that those producers who are 
giving us films which give steady projection are entitled to 
much credit for their painstaking care. 


Thickness of Film Stock. Film stock should be of the full 
standard thickness, since thin stock has decided tendency 
to produce unsteadiness of the picture. 

Standard Perforations. Perforations should, by all means, 
be of standard dimensions. Instead of that there are several 
sizes and shapes, and since the projector sprocket teeth, 
which engage with these perforations, are of necessity of 
standard dimensions, more or less trouble is encountered 
from this source. At this time (Dec. 15, 1915) the Motion 
Picture Board of Trade has just formed a "Bureau of 
Standardization," the first work of which is expected to be 
the standardization of film perforations. 

Damage to Film. Naturally an article so thin and fragile 
as film is susceptible to .damage. Film is easily torn in two; 
also it is easily scratched, particularly the emulsion. Its 
sprocket holes are subject to strain and to breaking and 
tearing. Most of the tearing is due to loose patches catching 
on sprocket idler rollers and to worn sprocket teeth and 
improperly adjusted projection machines. Nine-tenths of 
the scratching of film is due to poorly designed projector 
take-up tension and to "pulling down" in rewinding, the 
latter consisting in rewinding a portion of the reel loosely, 
then holding one reel stationary while revolving the other 
to tighten the film roll. Injury to sprocket holes is, in the 
main, chargeable to undercut and hooked sprocket teeth 
(see General Instruction No. 8, Page 462), and to too much 
pressure by the tension shoes of the projector. (See General 
Instruction No. 9, Page 463.) 

Operators, are, I believe, as a rule, reasonably careful in 
handling film. In many theatres, however, rewinding, thread- 
ing the machines and repairing film are made the duty of an 
irresponsible usher, or reel boy, and what he does to the 
film is all too often a shame to tell. Patches half and even 
three-quarters of an inch wide; patches without the emulsion 
scraped off, and patches as stiff as a board are too common 
to excite more than passing comment, and film spliced to- 
gether with pins and even nails are often sent back to the 
exchange. It is an outrage, but one which cannot always 
be laid at the door of the operator. Even when the operator 
does the rewinding and patching, he is, in all too many cases, 
expected to do it while projecting a picture, and hence must 
either neglect his projection or his rewinding and film repairing. 



Injury to the film in passing through the modern 'motion 
picture mechanism is invariably due to either the bad con- 
dition of the film itself, or to the laziness, carelessness or 
lack of knowledge of the operator, or to the false economy 
of managers who refuse necessary repairs to the machine. 


ARE RUNNING. Patches in which sprocket holes are not properly 
matched will climb the sprocket teeth, causing the loss of a loop, 
or will grip the teeth of the sprocket and wrap around it. Split 
sprocket holes will catch on an idler and a section of the edge 
of the film will be split off, if nothing worse. 

Emulsion deposits on tension shoes (See General Instruc- 
tion No. 10, Page 464) often does considerable damage to 
first run film. 

Mending the Film, i. e., making patches in it, is a matter 
which is of the utmost importance. Badly made patches are 
the cause of unending annoyance, as well as immense damage 
to the film itself. 

If the patch be made, in such manner that the sprocket 
holes do not match perfectly there is likely to be a jump of 
the picture on the, screen as the patch goes over the inter- 
mittent sprocket teeth, due to the fact that the hole is too 
small to allow the sprocket tooth seating properly therein. 
There is also the liability of (a) the hole locking on the 
upper sprocket tooth and, pulling the loop around under the 
sprocket, (b) The film running off the sprocket, (c) The 
intermittent sprocket climbing one or more holes, thus 
shortening one of the loops, making the other proportion- 



ately longer and throwing the picture out of frame, (d) The 
takeup tension pulling the film over the lower sprocket, thus 
losing the lower loop. All this is liable to occur also where 
one of the holes is properly matched, but the other is not, 
thus making one hole small and making the film, as a whole, 
crooked at that point. You will see, therefore, the impor- 
tance o-f matching the sprocket holes perfectly. 

In the operating room it is customary to make patches with 
the fingers. Film cement welds more than it glues the film 
together. Considerable pressure is therefore necessary to 
make a perfect joint; much more than can be given by the 
fingers alone. Also with the fingers the pressure cannot pos- 
sibly be applied evenly. Until recently there has been no 
film mender suitable for use in the operating room. 

ooo ooo o ooooo a 

Figure 75. 

To Make a Patch cut the film, as shown in Fig. 75, leaving 
a stub as shown at A. This stub should be not less than 
one-eighth inch and not more than three-sixteenths of an 
inch in length. The latter measurement is best, as it will be 
found difficult for the operator, usually working in a hurry, 
to make a good patch only one-eighth inch wide; but if wider 
than three-sixteenths the patch will be stiff. End B should 
be cut exactly on the dividing line between two pictures. 
Scrape every particle of emulsion off stub end A, and scrape 
about one-eighth inch on celluloid side of end B, to roughen 
the celluloid and remove all dirt and grease. A very 
sharp knife is best to scrape with. Some use the blade 


of a safety razor. Be sure to thoroughly scrape end B and 
to scrape every particle of the emulsion off stub end, A. 
Cement will not stick to emulsion. You must remember that 
the emulsion covers the entire film on one side, therefore be 
careful to get it all off around the sprocket holes. This is 
where many make their error in patching film. They scrape 
the center of the stub and the center of the back of end B, 
but do not scrape thoroughly around the sprocket holes, 
where the greatest strain will come. In consequence their 
patches soon come loose around the sprocket holes and there 
is trouble. The stub should be scraped to a straight line, as 
per dotted line, else there will be a flash of white light on 
the screen as the patch passes. It matters little whether 
patches be made as per C, or D, Fig. 75. Patches made 
one way will go through some projectors better when partly 
loose, and through other projectors loose patches will go 
through if made the other way. If the patch is in good' con- 
dition it will go through equally well either way it is made. 
Having scraped the ends clean, as directed, place them to- 
gether so that the sprocket holes exactly match (if patch is 
to be made with fingers), with the emulsion side of both 
ends either up or down that is to say, on the same side. 
Grasp one edge firmly with thumb and finger and apply 
cement, with the cement bottle brush, to the other. Clamp 
the cement edge down tightly, being careful the sprocket 
holes exactly match, with thumb and finger of other hand 
releasing opposite edge. Apply cement to other edge and 
clamp that also, applying all the pressure you can for about 
ten seconds or so, and the patch is done. Every cement 
bottle should have a small brush attached to the under side 
of its cork. When you buy cement accept none without the 
brush. It is put up that way now by many, and should 
be by all. 

Film Cement may be easily made. The following are a few 
formulas: For non-inflammable stock, one-half pound of 
acetic ether, one-quarter pound of acetone merch, in which 
dissolve six feet of non-inflammable film from which the 
emulsion has been removed. 

For inflammable film, a piece of film three inches long dis- 
solved in one ounce of acetic ether is a satisfactory cement, 
but it will not work on N. I. (non-inflammable) stock. In 
dissolving the film, in either case, first remove the emulsion 
and then cut the film into fine .strips. 


Acetone Cement. Four ounces of acetone; one-half ounce 
ether; six inches old film, from which remove the emulsion 
and cut into strips. 

Another Formula. Equal parts of amyl acetate and ace- 
tone. Will not turn white on film, and will not dissolve the 
film as ether will. Works on all kinds of stock. Best used 
with an all steel three flap film mender. Can be used by 
those making patches by hand if worked rapidly. Scrape 
film, use small camel hair brush; keep bottle tightly corked 
when not in use. 

Still Another. One ounce collodion; one ounce banana oil 
or bronzing liquid; one-half ounce ether. For Pathe hand 
colored films, one-half acetone and one-half ether. 

N. I. Cement. For non-inflammable film add one part 
glacial acetic acid to four parts of flexible collodion or to 
any of the film cements. It is satisfactory for either N. I. 
or regular film. 

Please understand that these are formulas sent in by opera- 
tors from time to time, and recommended by them. The 
author does not vouch for their excellence. 

Size of Reels. There has been some inclination to in- 
crease the size of reels to two and even three thousand feet, 
which is, I think, bad practice. With two projectors there is 
really no good reason why it should be done, and it is dis- 
tinctly objectionable for several reasons, one of which is 
that it increases the probable loss should a fire occur, as 
well as increasing the volume of fire and smoke. 

One thousand feet of film has been and should continue to 
be the standard reel of film. It is convenient to handle, not 
overly heavy, and keeps the fire damage risk within reason- 
able limits. But the reels themselves should be not less than 
12 inches in diameter. Personally, I believe a 14-inch reel 
having a 4-inch hub would be ideal from any and every point 
of view. The hubs of present reels are too small Small hubs 
and the old-style takeup tension are a combination which 
produce heavy strain on the first fifty to one hundred feet 
of film. But whatever is done in that direction, the reel should 
be of sufficient diameter that one thousand feet of the thickest 
film (yes, film stock varies slightly in thickness} will fill it to 
only within one-half inch of its outer diameter, assuming the 
film to be wound not too tightly. Thus the whole film will be 
protected by the metal sides of the reel. 


Overloading reels has been the source of much annoyance 
to operators in the past, but it is not so! much practiced of 
late. Apparently even the exchanges are slowly learning to 
exercise a little common sense, in some directions at least, 
in the care of their property. The evil of the overloaded 
reel is threefold: (a) That portion of the film outside, or 
above the sides of the reels is absolutely unprotected, there- 
fore liable to injury in many < ways; also it is likely to slip off, 
to the exasperation of the operator and possible delay of 
the show while it is wound on 'again, to say nothing of 
probable damage through contact with the more or less 
dusty, dirty floor, (b) The increased temptation to ! "pull 
down," and pull down good and hard, too, to get a^ much 
of the film inside the reel as possible, and (c) The fact that 
the film may rub against the magazine, thus scratching the 
film, and possibly interfering with the operation of the 
takeup, incidentally requiring a very tight takeup tension, 
which is bad indeed, and a prolific source of damage to the 
first part of the film through scratching and pulling 'out the 
lower loop. 

Leader and Tail Piece. It is for several reasons essential 
that there be a "leader" and an opaque tail-piece on every 
reel of film, including multiple-reel features. In the first 
place, the leader protects the title from damage. In thread- 
ing into the takeup it is frequently desirable, if not necessary, 
to fold an inch or so of the end of the film over on itself. 
By so doing it is made stiffer and is more easily thrust under 
the reel-spring. This means that the leader will occasionally 
break where it is folded; hence there will be gradual wasting 
av;ay. If this occurs on the title the damage is quite evident. 
Soon there will have to be a new title provided. If, however, 
it is only a leader that is being thus damaged, it is not 
serious. But there is another reason why leaders should be 
used, viz., in rewinding, when the job is done, the end of the 
film often flaps around anywhere from one to a dozen 
times before the reel stops revolving, and if there be no 
leader to receive the brunt of this rough treatment, the -title 
is injured. There is yet another reason which not only deals 
with the necessity for leaders, but also with their length. 
About 30 inches of film is required to thread into the takeup. 

If there be not enough leader, the title will be practically 
all on the takenp side of the machine aperture when threading 
is completed. In order that the run may commence with the 
first image of the title it is necessary that there be not less 
than 30 inches of leader. If the title be short, even this is 


not sufficient. -If a short title comes on the instant the 
machine starts it will be gone before the operator can frame 
up and adjust his light, unless the film be threaded in 
frame on the first title picture, or the leader be a blank which 
has been exposed in the printing machine and developed, 
thus leaving only the dividing lines, which may be used as a 
guide in framing. 

As a matter of fact, leaders should be of exposed film, 
developed very dense, ,and at least full four feet in length. 
This would give the operator time to frame up, adjust his 
light and have everything just right when the title comes 
on. Under these conditions if the machine be run slowly at 
the start the title would have to be very short indeed if the 
audience could not read it. As a substitute many houses 
show a stereopticon title slide before running the reel. I 
do not fancy this scheme. It savors of a makeshift. If 
things are as they should be there will be no necessity for a 
slide title, but in many cases it is unavoidable, and therefore 
better than nothing. 

"Ah ha!" I think I .hear some of you say; "you condemn 
the operator who does not thread in frame, yet now advise 
the use of leader which will allow of framing up after the 
machine has been started." 

Right you are, brother, but I don't make conditions. None 
but Mr. Sloppy Workman Operator will thread his machine 
out of frame, and frame after it has started, but unfortunately 
Mr. S. W. Operator is still a numerous tribe, and we must 
therefore take that fact into consideration and try to fix 
things so that his sloppyness (a crude term, I grant you 
but expressive} will do the least possible amount of harm. 

The reason for also advising leader and tailpiece on 
multiple-reel features lies in the fact that they will only 
slightly inconvenience the operator in the two-machine house, 
and will be a great convenience to the one-machine house 

I strongly advise managers to insist on leaders not less 
than 48 inches in length on all films; also that they be, if 
possible, of the kind showing dividing lines. If exchanges 
will not supply such leaders it will pay theater managers to 
buy blank film and use leaders of their own. 

It is important that there be a tailpiece on every film. It 
need not exceed 12 inches in length, but should by all 
means be there and should be of the opaque variety. When 
the light is shut off by the tailpiece the machine should be 
instantly stopped. Many operators have a most reprehensible 


habit of running the machine until the end of the film has 
passed over the aperture and the white light is on the screen. 
This instantly destroys all the illusion. It is in the nature 
of a most unpleasant shock, particularly if the audience be 
deeply interested in the picture. 

Stop your' machine while the tailpiece is. over the aperture. 
If there be no tailpiece, stop the machine -when the end of the 
film comes out of the upper magazine, before it has got past 
the aperture. Never, under any circumstances, allow white light 
to show on the screen. SUCH WORK is CRUDE IN THE EXTREME. 

Inspection. The operator should, so far as possible, re- 
pair all the damage he himself inflicts upon a film while it 
is in his possession. 

However, it is the duty of the film exchange thoroughly to 
inspect all films as they are received from theatres, and put 
them in A\ condition before they are again sent out. 

brother operator who gets them next, to repair the damage you 
do. You are in position to "pass the buck," true, but IT is NOT 


Perfect projection is impossible where a film is in imper- 
fect condition, and a film is not in perfect condition when it 
has wide, stiff, or loose patches, misframes, ripped sprocket 
holes, etc. These faults are prolific sources of imperfection 
in projection. 

It is a well known fact that many film exchanges make but 
the most superficial inspection of film and all too frequently 
no repairs at all. The underlying cause of poor inspection 
and repair of films is, I believe, the endeavor on the part 
of exchanges to get too much work out of a film, as well 
as an unwillingness to expend the proper amount of money 
in the employment of enough and competent inspectors. In 
many exchanges men or girl inspectors are employed, at low 
wages, and are expected to "inspect" anywhere from fifty 
to seventy-five reels of film a day, which is from two to five 
times (dependent on condition) as many as they can inspect 
and repair properly. 

In such exchanges the inspection very largely consists in 
running a film from one reel to another at top speed. The 
only faults ordinarily detected by this sort of performance 
are the very bad ones, such as long strings of ripped 
sprocket holes, a patch loose half way across the film, or the 
film torn entirely in two. MINOR FAULTS CANNOT POSSIBLY BE 



fact, and a most reprehensible practice, too, that exchange 
managers will often ship reels out to exhibitors without any 
inspection at all. This practice is often aggravated by the 
exhibitor, who, when in a hurry for reels, demands that they 
be given him without waiting for any inspection at all. It is 
also a fact that exhibitors who do this will frequently upbraid 
the exchange if the films are in bad condition, and will blame 
the operator if breaks occur and the show is stopped. When 
a film leaves the exchange in anything but the best possible 
condition a wrong is done to everybody concerned, from 
the producer to the theatre audience. The result of faulty 
exchange inspection is, so far as the operator be concerned, 
one of two things: either it falls to him to do a lot of work 
which is no part of his duty and for which he is not paid, 
inspecting the films and putting them into condition, or, as 
an alternative, the projection, and incidentally his reputation 
as an operator will suffer. 

I am well aware that the question of inspection and repair 
presents a problem of many angles, and one not at all easy 
to adjust. However, this I can say without fear of successful 
contradiction: there is absolutely no excuse whatsoever for 
the utterly miserable condition in which many films are 
received by the operator. 

/ am heartily in favor of operators demanding overtime for 
inspecting and repairing film when they are received in bad 
condition. It most emphatically is NOT a part of their duty, 
and by what process of reasoning a theatre manager justifies 
his demand that his operator, without any remuneration what- 
ever, do the work of an exchange inspector, I have never been 
able to understand. 

There is now on the market a film-fault detector, the in- 
vention of one Rosenfeld, through which a film may be run 
at tolerably high speed, and which will automatically detect 
all loose, wide or stiff patches, mis-frames, and other mechan- 
ical defects. This machine also has an appliance for making 
a patch, which joins the film properly, and insures a splice 
of uniform width from which the emulsion has been entirely 
scraped. It also at the same time cleans the film by passing 
it through a bath of chemicals and washing it with brushes. 
With such a device in existence there is no longer any ex- 
cuse whatever for the mechanical faults found, in greater 
or less amount, in nine out of ten films sent out by the 
average exchange. 

There is now on the market a neat little cutting plier with 
which broken sprocket holes may be notched as per Fig. 76. 


This is a tool which should! be in the hands of every ex- 
change inspector and operator. It is the invention of A. 

-irww9 ^s i i 

Figure 76. 

Jay Smith, Cleveland. The price is $2 and well worth it. 

Where to Keep Films. Film should be kept near the floor 
of the operating room, since near the ceiling it is much 
warmer. It should be kept in a metal box having compart- 
ments for each reel, and one compartment below to hold a 
wet sponge r water. The film should be treated with a little 
glycerine once in a while, but this is only accomplished by 
having the film in actual contact with the liquid, as per 
directions further on. The glycerine is for the purpose of 
keeping the film soft and pliable, which it does by reason of 
the fact that it has the property of rapidly absorbing mois- 

Should water, by any accident, be spilled over a reel of 
film, or it even be dropped in a pail of water, it may be saved 
from damage if unrolled very quickly, not allowing the 
emulsion, which will be quickly softened, to touch anything. 
But the unrolling must be done very quickly or the emul- 
sion will stick to the back of the film and pull off. This does' 
not apply to colored or tinted film, though even these may 
sometimes be saved by very prompt action. The writer once 
rescued a first-run film from destruction thus: He happened 
to be in the operating room after the show had closed for 
the night. In taking the last reel from the magazine it 
slipped from the operator's hands and landed in a pail of 
water, being practically submerged. He grabbed the reel, 
ran down stairs, handed the end to an usher, ran to the front 
end of the theatre, looped the film over a chairback, and 
ran back and forth until the whole film lay across the back 


of the seats. The emulsion became very soft in places, but 
next morning it was found that a total of less than five feet 
was damaged. The exchange men never knew of the 
occurrence until more than a month after, when they were 
told of it. 

Moistening Dry Film. Traveling exhibitors often find that 
a reel which has been a long time in use has become very dry 
and brittle. It may be remoistened and rendered pliable by 
unwinding into a large metal can, in the bottom of w'hich 
water has been placed, with a wire screen over it to keep the 
film from contact therewith. Cover tightly, set in a mod- 
erately warm place until the film is soft and pliable. Watch 
closely, however, since if made too moist the emulsion will 
stick to the back of the film when it is rewound. 

It is even possible to give a film a glycerine bath, as fol- 
lows: In a long, shallow pan place a solution of 30 parts of 
clear water to one part of glycerine. Make a drum of slats 
about six feet in diameter by about six feet long (for one 
thousand feet of film), and by revolving the drum draw the 
film very slowly through the liquid, winding on the drum with 
the emulsion side out. After the film is all on the drum, 
revolve it rapidly to throw off the surplus liquid, then con- 
tinue to revolve the drum slowly until the film is dry. It 
should not be used for two or three days. Perform this 
operation in a room entirely free from dust, or you may 
seriously injure your film. 

Due to lack of proper inspection it is usually advisable, 
where practical, to inspect the films at the theater before 
they are run. To do this place the reel on rewinder,. and re- 
wind it very slowly, holding the edges between the thumb 
and forefinger with pressure enough to cup it slightly. By so 
doing you instantly detect all stiff or loose patches. Cut out 
the stiff ones and remake. Cement all loose patches and 
notch all split sprocket holes. If more than two sprocket 
holes are missing on one side that is, in succession, of 
course cut the film and make a patch. Inspection pays, and 
an ounce of prevention is worth a pound of cure. Managers, 
however, should not expect operators to inspect films for 
nothing. Such work is no part of an operator's duty and 
should by all means be paid for, aside from the operator's 
regular salary. 

Stretched Film. Ignorance, poor judgment, or carelessness 
in the drying room or the use of wrongly designed drying 
racks or drums is also responsible for much trouble. Film 


which is wound tightly on an unyielding drying rack or drum 
will in all probability be badly stretched, and in consequence 
the picture on the screen will be unsteady. This fault 
usually may be detected by doubling two or three feet of the 
film back on itself, matching two sprocket holes and then 
seeing if the rest match. Stretched film will not fit the projector 
sprockets properly, hence will not produce a steady piciure on 
the screen. 

Operators using first-run film will often notice a tendency 
of the film to curl up, or "cup" edgewise, with a flat spot 
every few inches when the film is unrolled loosely. This 
is evidence that it has been dried on a drum covered with 
slats spaced as far apart as the flat spots occur. Such film 
will have a tendency to buckle more or less over the aperture 
plate, producing an in-and-out-of-focus effect on the screen. 
The buckling may or may not be sufficient to be readily de- 
tected in the picture, but it is pretty sure to be present in 
some degree where such film is used, and even< though you 
cannot detect a distinct change in the definition of the 
picture (the flat spots are usually not more than 6 inches 
apart, therefore the effect is too nearly continuous to be 
readily detected by the eye as a separate phenomena every 
time a flat spot goes through) each time a flat spot passes 
the aperture, the effect is there and manifests itself by an 
injury to the sharpness of the picture. See "effect of loss of 
definition," Page 152. From what I have learned from some 
of the oldest drying-room men in the business, film should 
not be dried on a drying frame, but be wound on a large 
drum, having round-face slats not to exceed one-half inch 
wide, spaced not more than two inches center to center, 
or, better yet, though the process of drying would be slower, 
the face of the drum covered solid. In either case the drum 
should be so made that as the film shrinks in drying the 
diameter of the drum will be decreased against the pressure 
of springs. 

I am not a film producer or drying-room man, but the 
foregoing seems to be based in common sense. It appears 
reasonable on the face of it. There is no manner of question 
but that film is often stretched in drying, and that f.he 
alternate cupping and flat spots are often present. Also there 
is no manner of doubt but that these things cause more or 
less trouble w>hen the film is projected. If the producer 
disputes the correctness of what is herein set forth, let bim 
set forth better reasons for the stretching and the cupping 


and flat spots, and then, since he will be convicted of knowl- 
edge of the cause, let him produce and apply the remedy. 

Emulsion May Be Removed from Film by soaking the film 
in warm water, to which ordinary washing soda 'has been 
added. Put in large double handfull of soda to the bucket 
of water. Wash the film afterward in clean, warm water. 


Cleaning film is an exceedingly important item in projec- 
tion. The rain marks you see are nothing more or less 
than slight scratches in the emulsion, which may or may 
not have removed that part of the silver carrying the image, 
but which have filled up with dirt, thus becoming either 
opaque or semi-opaque. With this dirt removed these 

scratches would for 
the most part be in- 
visible, or nearly so. 
I have seen a piece of 
film which was in lit- 
erally terrible condi- 
tion with reference to 
rain marks projected 
after a thorough clean- 
ing, and it was almost 
__ like a first run. 

Cleaning films with 

liquids, however, is not a thing to be undertaken without proper 
knowledge. Alcohol will remove the dirt, and will not injure 
the emulsion, but it is likely to cause the film to curl very 
badly, therefore it is not to be recommended for film cleaning. 
There .are now on the market two film cleaning fluids 
which have the approval and indorsement of the Projection 
Department of the Moving Picture World. These fluids have 
been thoroughly tested by the department editor. The film 
can be washed in these chemicals without injury. They do 
not cause the film to curl, and do in every way a satisfactory 
job. One of these cleaners is made by the Githcil Com- 
pany, New York City, and the other by the William Rhodes 
Film Company, Hartford, Conn. 

A less thorough method of film cleaning, but one more 
readily applicable, is found in the Mortimer Film Cleaner, 
illustrated in Fig. 77. This cleaner is designed to be fast- 
ened to the rewinding table between the reels. It opens on 



a hinge, and the film is drawn between two felt pads. This 
cleaner serves more than one purpose. It removes a con.- 
siderable quantity of dust and oil, and by so doing improves 
the projection. It also detects loose patches and as a rule 
pulls them in two, which is much better than having them 
pulled in two in the projector, thus stopping the show. If 
this little cleaner were used continuously in all theatres it 
would do much to improve results on the screen, but in 
order to get the greatest amount of benefit from a device of 
this kind the film must be subjected to the process contin- 
uously; that is to say, at each rewinding. Results would also 
be improved if one of the clean- 
ing fluids named were used in 
conjunction with the Mortimer 

Another excellent device for 
cleaning film is the Ideal Film. 
Cleaner, shown in Fig. 78. 
This device consists of base 
casting D, carrying arm A upon 
which are mounted spools B-B. 
Upon each of these spools is 
wound a strip of cotton flannel 
9 feet long. 

The way the film passes 
through the machine is very 
clearly shown. Arm A is car- 
ried at its lower end by a spin- 
dle attached to the upper end 
of base casting D, and is held 
in upright position by a coil Figure 78. 

spring, so that when the re- 
winder is started with a sudden jerk or from any other 
cause the tension becomes too great the upper spool is pulled 
down slightly against the pressure of the spring, thus lessen- 
ing the tension on the film. Under screws C-C is a coil 
spring which holds spools B-B over against arm A. In the 
caps of the other end of spools B-B are six holes similar to 
those seen in front caps, and one of these holes engages 
with a dowel pin in arm A. When a section of the cloth 
becomes soiled all that is necessary to bring a new strip 
into place is to pull outward on either one of the spools 
against the pressure of the coil spring, which releases the 
spool from the dowel pin, whereupon you can revolve it and 


bring a new surface of cloth against the film, snipping off 
the soiled piece with a pair of shears. 

' I think the action of the device is made clear by this 
explanation and the photograp'h. Both the Ideal .and Morti- 
mer have the approval of the Projection Department of the 
Moving Picture World, and one of these devices ought to be in 
every operating room, since it will be worth its price merely 
for the removing of oil from the film. 


Burning film leaves a sticky, brown colored gummy sedi- 
ment on metal. This may be instantly removed by washing 
with ordinary peroxide of hydrogen, which may be had in 25 
cent bottles at any drug store. 


There have been many inquiries with regard to the "life 
of film," that is to say, those interested have wanted to know 
the length of time a negative or positive print could be pre- 
served in usable form. The only authentic information I 
have been able to obtain is contained in the following ex- 
cerpts from letters received from the Eastman Kodak Com- 
pany, the Vitagraph Company, and the Lubin Manufacturing 
Company. The Eastman Kodak Company says: 

"We cannot give you information which could be considered 
as absolutely authentic, but from the experience we have had we 
believe it is possible to keep processed film, both negative and 
positive, with but slight fear of deterioration, provided the 
proper amount of precaution be used. In the the first place 
it is absolutely imperative that all traces of the hypo be removed 
in the developing process before the film is dried; secondly, 
there should be no contact with any metal in any way, either 
by being wound on a metal reel or stored in the usual tin 
containers. The film should be tightly wound and then 
wrapped in tissue paper, with an additional oil tissue outer 
wrapping, and then placed in a wooden box, which in turn 
may be stored in a vault or safe, or placed where the atmo- 
sphere is of normal temperature and humidity. It might be 
well in winding the film to see that no unusual amount of 
moisture is wound into it. This small amount of informa- 
tion is about all we have on the subject, but if the foregoing 
be carefully carried out there is every reason to believe that 


the film will remain in a state of excellent preservation for 

Mr. J. Stuart Blackton of the Vitagraph Company says: 
"On the fourth of July four years ago our New York office 
was burned, and all the old films we had been keeping in a 
large iron safe, in hermetically sealed boxes, were destroyed. 
It is my opinion, however, that films of the present make, 
if sealed up in air tight boxes, would keep for a very long 
time. However, all the films over ten years old that I have 
seen and tried to run on a machine were very brittle and in 
such bad shape that it was almost impossible to keep the 
picture on the screen, this being due, no doubt, to the fact 
that they had not been kept from contact with the atmo- 

Mr. Siegmund Lubin, president of the Lubin Manufac- 
turing Company, says: "So far as the writer knows, a nega- 
tive will keep indefinitely; that is to say, the way we keep 
negatives, viz: by winding them in small rolls, placed in 
small cans having lids. We have found negatives which we 
have had sixteen, seventeen and eighteen years to be in 
practically the same condition now as when they were taken, 
with a possible exception that they might be a trifle darker, 
though not enough to affect the negatives seriously." 

This seems to be, up to date, the only available informa- 
tion. It comes from gentlemen who are perhaps best com- 
petent of judging, but even they are uncertain as to the 
exact facts, only one advocating hermetically sealing 

I would presume that the advice of the Eastman Kodak 
Company with reference to the method of packing would be 
best. They are in the film manufacturing business, and may 
be presumed to have superior knowledge of the best method 
of treating their own product. I might add to this by say- 
ing that I have myself seen film which was fully ten years 
old, and which had received no particular special treatment, 
yet seemed to be 1 as pliable and in as good condition as the 
day it was made. 

Summing up the whole matter, my own belief is that at 
or near sea level, where the atmosphere contains the ordinary 
amount of humidity, films packed according to the sugges- 
tion of the Eastman Kodak Company would keep in prac- 
tically perfect condition for at least fifteen years ; beyond that 
it would be merely a matter of speculation. However, the 
caution with regard to thorough washing out of the hypo is 
highly important. The east trace of hypo would, in the 
course of years, cause stains which would ruin the picture. 



The Edison, Power, Simplex, Motiograph, Standard and 
Baird projection machines all pass exactly one foot of film 
to each turn of the crank, so that the number of feet in a 
reel may be measured by running it through one of these 
machines and counting the number of turns of the crank, 
which will equal the number of feet in a reel. 

Figure 79. 

In Fig. 79 a film-measuring machine is shown; the pic- 
ture is self explanatory. This particular machine is made by 
the Nicholas Power Company. Several American makes of 
film measurers are on the market as well as instruments of 
English and French manufacture. 

A very good film measurer may be made by disconnecting 
the intermittent of a standard projector, using only the upper 
sprocket one turn of the crank, one foot of film. 

The Operating Room 

MORE and more the moving picture theatre owners and 
managers are coming to recognize the proposition 
that not only is it necessary to good results that the 
operating room be equipped with up-to-date appliances, but 
also that the room itself be commodious, carefully constructed, 


and supplied with running water, as well as with thorough 
ventilation. The following may be taken as the essentials 
of a first class, up-to-date operating room: 

1. It should be located central, sidewise, with regard to 
the screen, and as nearly as possible so that its floor will be 
3 feet below the level of the center of the screen, though a 
considerable pitch in projection will not seriously mar the 

2. It should not be placed nearer to the screen than 50 
feet, and may be placed as far away as 250, or even 300 feet, 
though 125 should be the maximum, since above that dis- 
tance it becomes difficult to match up the optical system of 
the projector so as to give the best possible results for the 
power consumed. 

3. It should be absolutely fire-proof in every respect, hol- 
low tile, concrete or brick being the best materials for the 
construction of the walls and ceiling, and concrete with 
cement finish best for the floor. Asbestos millboard on a 
substantial angle-iron frame makes a fairly good room, if 
properly constructed, though it does not compare at all favor- 
ably with concrete, brick or hollow tile. One objection to 
this form of construction is that it is very far from being 
sound-proof, so that a noisy economizer or projector, re- 
winder, or even talking in the operating room is apt to be 
annoying to the audience. Rooms of this kind should have 
double walls and ceiling, separated by an air space. When 
the walls are of concrete or hollow tile I would strongly 
recommend that the ceiling be of the same material. 

4. It must have a solid foundation, since the least vibra- 
tion in the floor will inevitably affect the picture on the 
screen. You absolutely cannot have a shaky operating room 
floor and a steady picture on the screen. 

5. It should be as nearly as possible sound-proof, to the 
end that the noise of the machines, rewinding, or anything 
else that goes on in the operating room will not annoy the 
audience. This is of much importance. 

6. It should be provided with sufficient incandescent lights, 
arranged to instantly and brilliantly illuminate all parts of the 
room; also there should be an extension cord, with a lamp, 
provided with a guard, which may be carried to any point 
in the room. 

7. It should be reasonably easy of access, preferably not 
opening directly into the auditorium, and should be reached 
by a stairway, rather than by a ladder. If it opens directly 


into the auditorium, then the stairway or ladder should be 
surrounded by some sort of partition, so that in case of fire 
the operator can leave the room without letting a cloud of 
smoke into the auditorium to terrify the audience. 

8. It should be large enough to hold all apparatus and still 
allow not less than two feet (three is better) in the clear 
behind the machines after they have been set far enough 
back from the front wall so that the operator can pass be- 
tween the lens and the wall, with not less than 6 feet in 
width for a single machine and three additional feet for each 
additional projector, stereopticon or spot light. The ceiling 
should be as high as possible the higher the better, within 
reason, of course, but should in no case be less than six and 
one-half feet in the clear. That should be regarded as an 
absolute minimum, but less than seven is very bad. 

9. All openings should be equipped with fire-proof shut- 
ters which will close quickly and automatically in case of 
fire, except the vent flue, which must be unobstructed if there 
is a fan, and if of the open type must have a damper weighted 
to remain normally open, as will be hereinafter explained. 
The observation port should be fitted with a movable shutter 
which can be raised or lowered to suit the convenience of 
the operator, as will be set forth further along. 

10. There should be a vent flue leading as nearly as pos- 
sible directly to the open air above the roof. If of the 
open type this flue should have an area of at least 288 square 
inches, regardless of the number of projectors used or the 
size of the room. There will be just as much smoke from 
a film burning in a small room as from one burning in a 
large room. If a fan is installed in the vent flue then it 
should be large enough to accommodate a 16-inch fan. There 
should be a separate vent flue in the rewinding room, if 
there be one, of the same dimensions as the one in the main 

11. The interior walls and ceiling should be painted with 
a very dark or black flat paint paint without any gloss. 
This is important because of the fact that the darker the 
operating room the better able will the operator be to see the 
shadows in his picture. 

12. All wires should be in conduit, and 'the conduit system 
thoroughly grounded. Fuses and switches should be in metal 
cabinets, or in cabinets built into the wall and covered with a 
metal facing. Conduits should, where possible, be built in 
the walls, and conduits leading to the projectors should be 


carried under the floor to a point immediately under the 
lamphouse of each projector. 

13. Iron lined operating rooms should not be allowed, but 
if they are, then the floor should be covered with a good 
insulating floor covering, such as cork matting, rubber mat- 
ting, or heavy linoleum. 

14. The room should contain nothing except the things 
necessary to the work of projection. 

15. There should be proper tool racks and closets for each 
operator's clothes and tools, a substantial work bench with 
a good vise, though this need not necessarily be located in 
the operating room. 

16. The arrangements should be such that all apparatus, 
switches, etc., will be easy of access to the operator, both 
for manipulation and repair. It never pays to make things 
unhandy. On the contrary it does always pay to arrange 
them conveniently. 

17. It should contain only the most up-to-date apparatus, 
and that apparatus should be kept in perfect condition. 
It should (and this is of paramount importance it cannot be 
too strongly emphasised} have observation ports of amply large 
proportions so that the operator may have a clear, unobstructed 
view of the entire screen, either when seated or standing in oper- 
ating position. This may be readily accomplished by installing 
a special sliding port shutter, as will be hereinafter explained. 

18. The exterior of the room should be as inconspicuous as 
possible; that is to say, it should be decorated to harmonize 
with the rest of the theatre, or, if possible, to form some 
ornamental part in the general scheme of decoration. 

19. It should be placed in charge of a thoroughly competent, 
reliable staff of operators, possessed of both practical and tech- 
nical knowledge of the art of projection, supplemented by a 
good fund of horse sense. No application for position as oper- 
ator should be considered unless the applicant can show that he 
has had at least one year's experience, or has served one year's 
actual bona fide apprenticeship in an operating room. 

The foregoing constitutes what might be termed the funda- 
mental essentials of operating room construction and equip- 
ment, but a detailed explanation is essential in addition to 

Operating Room Door. The door of the operating room 
should not be less than 2 feet wide by 6 feet in height, and it 



must, of course, be of fire-proof material. The sliding door held 
normally closed by gravity is best. This idea is illustrated 
in Fig. 80. 

Figure 80. 

Operating Room Floor. It is of extreme importance that 
the operating room floor be perfectly solid, rigid and entirely 
free from vibration. 


Figure 81. 

Suppose for instance your operating room floor vibrated 
evenly all over just 1/64 of an inch. This means your whole 
picture is jumping up and down on the screen precisely that 
much, and on the whole this would scarcely be perceptible. 


On the other hand, however, let us suppose the floor vibrated 
in such manner as to move the lens of the machine up and 
down in teetering fashion the same amount. Assuming a 
throw of 100 feet the movement would then be very percepti- 
ble indeed on the screen. It is illustrated in Fig. 81, in which 
A is the crater of the arc and B the objective lens. If you 
move A down 1/64 of an inch and at the same time move B 
up 1/64 of an inch you will readily see what will happen out 
at the screen surface one hundred feet away. The dotted 
line illustrates it. 

Modern practice is to fill in with not less than six inches 
of rich concrete and after tamping this down well finish the 
top off with one inch of cement, the same as is used for 
sidewalks. But let me caution you that many contractors 
will use a cheap cement unless you specify the kind and see 
that it is used. The result of using this cheap cement is that 
it constantly wears away into dust, thus keeping everything 
in the operating room covered with dirt. I tyave seen many 
operating rooms made that were nothing short of an outrage 
in this respect. The only remedy was to paint them with 
oil paint. It is also well to see that the cement finish is 
mixed with sand in proper proportions. Remember that, 
strange as it may seem, not all contractors are followers of 
the Golden Rule, and sand is cheaper than cement. Also 
after the job is done the novice cannot detect the swindle 
at once; he may never detect it, in fact, but simply knows 
there is something wrong with the operating room floor. 

If the floor is built of concrete and cement, and the precau- 
tions I have named are taken, it will to all intents and pur- 
poses be one solid block of stone when it has set, and you 
won't have any vibration at all, because a thing of that kind 
is too heavy to vibrate. 

Ports. There must be one observation and one lens port 
for each projector, one lookout and one lens port for the 
dissolver, if there is one, and a combined lens and observa- 
tion port for the spot light, except that if the projector be a 
combined picture projector and dissolving stereopticon, then 
it must be provided with two lens ports, one small and square 
or round, and one narrow and high. 

Locating Lens and Observation Ports. There is a right 
and a wrong way and a hard and an easy way to do almost 
everything, including the locating of lens holes. The author 
has seen it done in many different ways, but the following 
method "seems, everything considered, easiest and best. 



If observation port holes are built into the wall and made 
of the right size, it will require extremely accurate work 
more accurate than is likely to be done by the average brick- 
mason, concrete or hollow tile man to get them exactly right. 
I would strongly recommend the following procedure. 

Lay out your operating room wall as per Fig. 82, in which 
A, B, are machine lens ports, and C, D, observation ports, the 

Figure 82. 

NOTE: Through an oversight the stereopticon observation port was 
omitted. It should be 8" square, located at convenient height, its 
center about 5' 6" from the floor. 

latter designed to be covered by a sliding port-shutter, and 
E the stereopticon lens port. It will be observed that ports A 
and B are 12 inches square, and that port E is 18 inches 
high by 8 inches wide, which is, of course, far in excess of 
actual requirement. 

Taking, for example, the Simplex projector with standard 
pedestal; when it sets level its lens is 47^ inches from the 
floor, and this is approximately the height of the lens of 
other modern projectors. It will be observed that ports A 
and B are located 3 feet center to center, and that their cen- 
ters are 18 inches on either side of the center line of the 



screen, which must be first located on the plan. It will also 
be observed that the bottom of ports A, B is 3 feet from the 
floor, which brings their center 42 inches above the floor line, 
whereas the lens will be 47/^2 inches from the floor. In 
most cases, however, there is a more or less steep pitch in 
the projection, so that, in ordinary cases, if the projector be 
located with the lens 20 inches from the wall, as it should 
be, the light ray will strike approximately the center, or even 
below the center of the large port. 

After the wall has been built, the floor finished, projectors 
in place and the light finally projected to and located on the 
screen, and the machines per- 
manently bolted down, insert 
a piece of asbestos millboard, 
3/8 or 1/2 inch thick, set flush 
with the outside edge of the 
wall, as per A in detail sketch, 
Fig. 83, strike the arc, project 
the light ray on this board, 
mark a circle around the light, 
cut out the circle, replace the 
board in the opening and ce- 
ment it in as per detail sketch 
Fig. 83. 

Having completed this, set 
another board, C, Fig. 83, flush 
with the inside edge of the Figure 83. 

wall, and proceed as before. You 

will then have your lens port in exactly the right location 
and precisely the right size, and you will have it, too, with 
a minimum amount of trouble. 

The observation ports C and D, you will observe, are 12 by 
24 inches,, with their bottom located 4 feet from the floor 
line, and their center 16 inches from the center of the lens 
port. These ports are designed to be covered by an asbestos 
millboard, or metal sliding shutters, as per Fig. 86, the detail 
of which, together with detail of grooves, is shown in Figs. 84 
and 86. 

Port E, Fig. 82, is the stereopticon lens port, and is treated 
the same as ports A and B, except that there will be two 
small light ray holes in the asbestos millboard, instead of one. 

This is the easiest method of locating the lens ports, and 
it will be found to serve perfectly, I think, except in very 
rare cases where there is a perfectly level projection, in which 



case ports A and B should be located 6 inches higher, or 
where there is an extraordinary steep pitch in the projection, 
in which case ports C and D must be located lower, as pos- 
sibly must also ports A and B. 





Figure 84. 

In cases of very steep projection the height of the ports 
may be located as per Fig. 84. First locate the height of the 
operator's eyes when seated in operating position. I have 
assumed this to be 4 feet from the floor and 3 feet away 
from the wall, at A, Fig. 84. Now measure the exact dis- 
tance from Point A to the bottom of the screen, using the 
elevation plan of the theatre, if there is one, also the exact 
vertical height from the bottom of the screen to point A, 
Fig. 84. Draw a rough plan, to scale, by laying off the 
height of the operator's eye above the bottom of the screen, 
and the horizontal distance to the screen. Then draw line S, 
Fig. 84, extending from point A to bottom of the screen. 



Having done this, measure from the operating room floor 
line straight up to where line S bisects the line of the front 
operating room wall, and that will be the bottom of your 
observation port, though you should make it two or three 
inches lower than the actual measurement from the floor to 
the line. The lens ports may be laid out in exactly the same 

Still another way is by calculation. This, too, is shown 
in Fig. 84, in which I have assumed that the bottom of the 
screen is 20 feet below point A, and 80 feet away. Divid- 
ing 80 by 20 we find there is a drop of one foot in each four 
feet of horizontal distance, so that by measuring four feet 
horizontally from point A we establish point T, and then 
measuring down vertically one foot we get the exact pro- 
jection pitch, and thus know where to locate the bottom of 
the port. 

For all ordinary cases, however, the plan first described 
will serve. 

Figure 85. 


The hole in the wall itself should in no event be less 
than 12 inches wide. The necessity for a wide port is illus- 
trated in Fig. 85, in which A represents the eyes of the 
operator located, when seated or standing in normal opera- 
ting position, from 2 to 3 feet back of the operating room, 



wall. B-B is the screen; lines X-X represent the view the 
operator should have of the entire screen, and would have 
did the width of the port extend from C to D; lines Y-Y 
show the view the operator actually has of his screen if the 
port is narrow and only extends from E to F. In this event 
he is compelled to bring his eyes right up close to the opening 
in order to see the entire screen, and that is a bad condition, 
from any and every point of view. 

/ know of no other one thing which operates to produce poor 
results on the screen to as great an extent as do narrow and 
badly placed observation ports. 

Figure 86. 

With his eyes right up close to the wall, the operator must, 
of necessity, at least to a certain extent, neglect his projec- 
tion machine and his lamp. Moreover: 

No operator wilt stand for hours with his face glued to the 
wall, watching his picture continuously; and unless it is watched 
continuously and closely there will be shadows on the screen, or, 
in other words, there will be faults in the projection. 

That is a proposition which is not a subject for argument. 
It is a statement of fact, which managers will do well to rec- 
ognize and consider very seriously. 


The height of the observation port is a much harder mat- 
ter to determine. If the ceiling of the room itself be high 
enough to allow of the installation of a sliding port, such as 
that illustrated in Fig. 86, I would strongly recommend that 
the hole in the wall be 12 inches wide by 24 inches in height, 
as per Fig. 82, and that over this hole there be installed a 
movable sihutter made of ^ or y 2 inch asbestos millboard, 
or of metal, if preferred, although asbestos board is better, 
behind which should be installed the regular asbestos or 
metal fire shutter, both sliding in grooves, as shown in Figs. 
84 and 86, the movable shutter to be hung on a counter- 

In Fig. 86 the shaded portion represents the movable 
shutter, also shown at B, Fig. 84. It should be at least 
14 inches wide, with an opening not less than 6 by 12 inches. 
I believe the illustrations make the matter perfectly clear, 
but in order to use this kind of shutter it is necessary there 
should be head room above the opening in the wall sufficient 
to allow the shutter to be raised so that upper edge of open- 
ing Y, Fig. 84, will come to the top edge of the hole in the 
wall at Point Z, Fig. 84, and the lower edge of opening Y 
go down to the lower edge of the hole in the wall. It is not 
necessary that this shutter raise or drop far enough to en- 
tirely close the opening in the wall, that being taken care of 
by fire shutter G, Fig. 84. 

In Fig. 84 the grooves in w.hich the shutters slide are 
omitted in the main drawing in order to show other things. 
They may be made from small angle and channel iron, 
readily obtained from dealers in structural iron. Any hard- 
ware dealer can obtain them for you. What is perhaps the 
most convenient method is to secure about 12 feet of \%- 
inch angle iron and the same amount of ^2-inch channel 
iron for each 24-inch observation port, and, after cutting 
to proper length, bolt the channels to one side of the angle 
as at R, Fig. 84. This leaves the other side of the angle to 
be fastened to the wall. If properly put together this makes 
a most excellent shutter groove. The one shown at R, 
Figs. 84 and 86, is designed to carry the movable port shutter 
and the fire shutter behind it. For single grooves one-inch 
angle iron, is ample. 

The whole idea of the movable shutter is to allow port Y, 
Fig. 84, to be placed in any desired position, to suit a tall 
or short operator; also to accommodate a man when either 
sitting down or standing up. Many authorities Insist on the 


observation port being not more than 4 or 6 by 12 inches. 
Now, a fixed port 4 or 6 inches high would be extemely awk- 
ward, since if placed to fit a five-foot man would be mighty 
bad for a six-footer, or vice versa, so they try to get around 
that difficulty by standing the thing on end, with result as 
shown by lines Y-Y, Fig. 85. The movable shutter enables 
the theatre owner to comply with the demands of the au- 
thorities in this respect, and still have a port which is excel- 
lent in every way. It is a shutter which appeals to common 
sense, and no official can possibly advance any valid objec- 
tion to it. 

The careful planning and locating of the observation ports, 
as hereinbefore set forth, will require a little thought and con- 
sume a little time, but if you locate them in such manner that 
the operator will be continuously inconvenienced you have no 
right to expect that you will have uniformly high class results 
on your screen, and let me tell you you probably won't have 
them either. 

A little time spent in careful, intelligent study of this mat- 
ter of planning and locating the observation ports will place 
the operator in position to give you much better service, and 
he will do it, too. Therefore it naturally follows that the 
time thus expended is a most excellent investment. 

The stereopticon observation port is not of so much im- 
portance, and a six or eight inch square or round hole will 
do, since, ordinarily, one uses the stereo but a few minutes 
at a time, and can put up with some inconvenience if neces- 
sary. The stereo lens port can be located the same as per 
directions for the projection machine lens holes, but in the 
case of the stereopticon the hole in the wall need not be more 
than 8 inches wide, but it should be 18 inches high, the same 
to be filled in with asbestos board afterward, as directed 
for the other lens ports. 

The spot light port, if one there be, should be located with 
its center 5 to 5^2 feet above the top of the floor, and should 
be 16 to 18 inches in diameter, square or round, as preferred. 

Wall Fire Shutters. Every observation port and vent 
opening should be provided with a fire shutter made of 3/8 
inch asbestos millboard, although some authorities are satis- 
fied with 16-gauge sheet metal. Metal is, however, not as 
desirable, I think, as asbestos board for this purpose. 

In Fig. 87 is shown the proper method of bracing the 
wall shutters to keep them perfectly flat. The braces are of 



1 by J4-inch iron secured to the shutter either by short, 
heavy screws or stove bolts. 

The proper installation of these shutters together with an 
adequate vent flue and thoroughly fire-proof walls offers 
not only absolute protection from fire damage to anything 
outside the operating room, but also against the probability 
of alarm on the part of the audience. This latter will 
not be accomplished, however, unless the fire shutters be so 
made that they will close the 
instant a fire starts. This last is 
of supreme importance. It is 
seldom indeed the fire itself 
which causes loss of life or in- 
jury to an audience. It is the 
panic which almost invariably 
follows an alarm of fire where 
an audience is gathered. Ninety- 
nine times out of every hun- 
dred there are abundant time 
and opportunity for every one in 
the theatre to escape with perfect 
safety, provided the audience 
acts rationally, but the fact is an 
audience seldom or never does 
remain rational or sensible when 
an alarm of fire is given, par- 
ticularly if either fire or smoke 
be visible. Given a glimpse of 
fire or smoke, as a general 
proposition you may depend 
upon an audience to go stark, 
raving mad, pile up in a heap 
and kill each other through 
trampling or suffocation. 

/ desire to strongly impress 

upon architects and moving picture managers and owners that 
it is entirely practical and feasible to prevent any glimpse of 
fire or smoke by the audience when a film catches fire, but in 
order to accomplish this fire shutters must be installed which 
will automatically" close every opening in the operating room 
wall the INSTANT the fire starts. 

Depending upon the operator to drop the shutters is by no 
means a safe proposition. The operator is but human, and 
when the film catches fire he is very likely to become more 

Figure 87. 



or less excited, and it is a cold fact that you never can tell 
what an excited man will do, or what he won't do. Therefore 
I emphasize the fact that it is a dangerous mistake to allow 
the installation of fire shutters in any other way than approx- 
imately as hereinafter described. 

Fig. 88 is a diagrammatic representation of the front 
operating room wall. The door is not located in the front 
wall because it should be there, but merely for convenience 
in showing the proper arrangement of the master-cord, which 
should terminate in ring A, held by an ordinary heavy spike, 

Figure 88. 

nail, or bolt, driven into the wall beside the latch of the 

This whole proposition hinges on the kind and location of 
the fuse links. The master-cord is cut into sections, and these 
sections are joined together with fuse links, located over each 
machine magazine, the film box, and over the rewind table in 
the rewind room. These fuse links may be of 160 degrees fuse 
metal, but preferably should be of film, as shown in Fig. 88, 
in which the fuse clamps are drawn out of all proportion as to 
size in order to show the thing more clearly. 

In Fig. 88 the dotted line represents the master-cord, 
which is stretched from point A to point B, as shown, though 
the cord may be carried in any other convenient way, pro- 
vided only that the links be located with relation to the 
machine magazines, film box, and rewind substantially as 
shown. The master-cord may be of heavy cord of such nature 



that it will not stretch, or it may be of No. 22 copper wire, 
provided some unthinking official does not object, The film 
links over machine magazines should not be more than 12 or 
less than 6 inches long, and should not be more than 3 inches 
above the top of the magazine. The same is true of the link 
over the film box. The one in the rewind room may be of 
convenient length, but there must be distance enough between 
clamp Y and insulator Z to allow the master-cord to slack 
sufficiently to let all the shutters go clear down. If this distance 
be too small there is danger that clamp Y will strike hole Z 
before the shutters have entirely dropped. 

Figure 89. 

The detail of the method of clamping the film to the cord 
is shown in Fig. 89, as is also the details of one method of 
attaching the fuse link over the upper machine magazines. 
Rings should not be used in place of angle studs X, because in 
that case when the film lets go the clamp might catch in the 
ring and prevent the shutters from dropping, whereas with 
angle studs when the master-cord slacks it instantly drops down 
off the studs. 

If metal fuse links are used they should be located ap- 
proximately the same as the film links shown. Angle studs 
X may be made by obtaining heavy screw hooks, such as 


housewives use to screw into the ceiling to hold the family 
bird cage,, etcetera, but the hook should be straightened out 
until it stands at approximately right angles to the screw, 
and the end should point downward, not up, when it is final- 
ly in position. The upright bolt attached to the magazine 
around which passes the film link, or the master-cord if a 
metal link is used, should be made of ->6 or l / 2 inch iron, 
flattened at one end and attached to the magazine by stove 
bolts, as shown. 

Having arranged our shutter cord the rest is simple. The 
individual shutters are raised and attached to the master- 
cord by their own individual cords, which terminate in a 
hook designed to attach to the master-cord. The master- 
cord remains permanently in place. It is never touched 
except possibly to tighten it if it gets slack. The shutters 
are raised one at a time in the morning and lowered one at 
a time at night. 

I believe that with what has been said and the aid of Figs. 
88 and 89, you will be able to understand this matter thor- 

The whole proposition is to place the fuse links where a 
fire, either af the film box, the rewind table or at either 
machine, will INSTANTLY strike one of them, thus sever- 
ing the master-cord and dropping all the shutters before there 
is any smoke or blase visible to the audience. Incidentally, how- 
ever, it is exceedingly important that the bottom stop upon 
which the shutters fall be heavily padded with shredded 
asbestos, since if the shutters fall on anything hard they 
will make an awful clatter and direct the attention of the 
audience straight to the operating room the very last thing 
to be desired. 

It will be observed that by this system the operator can 
also drop the shutters, since ring I is placed on a headless 
spike right beside the latch of the operating room door. If 
the vent flue be of the open type, then shutter D should be 
we : '4'hted so that it will remain normally open, and it must 
only be allowed to be closed by a cord attached to the 
master-cord by means of a hook, the result being that when 
the master-cord is slacked and the shutters closed the 
damper automatically swings open. 

An operating room thus equipped is, I firmly believe, as 
safe as it is possible to make it. 

There is no earthly sense in installing metal fuse links in 
the shutter cords, and locating these links at or near the ceiling, 


as is done in nine cases out of ten. Should a fire occur with 
the fuse links thus located, by the time they become sufficiently 
heated to melt there would probably be very little use in closing 
the shutters at all, because the audience would most likely have 
seen the smoke and blase and be piled up in a heap, climbing 
over each other in their mad endeavor to escape a fancied 

There are those who may argue that the shutters should 
be dropped gently, and that this can only be done by the 
operator; that if dropped suddenly as by a fuse melting, 
there will be a slam which is likely to attract the attention 
of the audience to the operating room, since even with the 
shutters falling on pads there is bound to be some noise pro- 




Figure 90. 

duced when from two to eight shutters are released and 
allowed to drop unrestrained. 

This is a matter concerning which there may well be hon- 
est difference of opinion, but the writer strongly favors very 
careful padding of shutters, as per Fig. 90, and carefully 
placed fuses, because there is always the liability of an ex- 
cited man forgetting to drop the shutters; also if the oper- 
ator is to be depended on why place any fuse at all? Better 
make it one thing or the other, and I believe fuses are the 

The Vent Flue. The vent flue of the operating room is an 
exceedingly important matter, since it not only provides ven- 
tilation, but must be depended upon to carry the fumes and 


smoke from burning film, should a fire occur. The vent 
flue should, where possible, pass directly from the operating 
room ceiling through the roof to the open air, with its top 
not less than 3 feet above the roof and protected by a suit- 
able hood to prevent rain from beating in. For a long time 
the author favored the open vent flue, as against the instal- 
lation of a vent-flue fan. However, further and careful study 
of the subject has changed his views. This change was 
largely brought about through realization of the fact that 
under certain conditions it is quite possible the draft through 
an open vent would be down instead of up; this is especially 
true in certain locations, or when the wind is in certain 
directions, as any housewife who has experience of a smoky 
chimney can testify. This being the fact, I am convinced 
that a fan in the vent flue is better than an open pipe. 
//, however, the vent pipe is of the open type it should have 
an area of not less than 288 square inches, regardless of the 
size of the room. A burning film will make just as much smoke 
and gas in a small room as it will in a large one. It should be 
provided with a damper, weighted to remain normally open, and 
only allowed to be held closed by a cord attached to the 
master-cord of the fire shutters in such manner that when 
the fire shutters are closed the vent flue damper automatically 
will swing open. 

If a fan is installed in the vent pipe it should be not less 
than 16 inches in diameter and it would be exceedingly good 
practice to install two vent pipes and two fans instead of one, 
so that in case one of the fans gets out of order there will 
still be the second one to fall back on. This may seem like 
a rather expensive precaution, but somehow or other it 
seems to be a fact that when a thing happens it usually hap- 
pens just as the wrong time, which, applied to the single vent 
flue, would mean that a fire would most likely occur when 
the fan was broken down. 

It is essential that the vent flue, if made of metal, be thor- 
oughly and completely insulated from any inflammable sub- 
stance throughout its entire length, since it is likely to get 
very hot if there is a serious fire. The safest plan is to 
make a double pipe, with an air space not less than 3 inches 
between the inner and outer walls. 

Operating Room Ventilation. The ventilation system of 
the operating room is a matter of much importance. It must 
be remembered that the operating room is often located 
immediately under the roof of the building and in any event 


would be extremely hot in summer time. Add to this the 
heat generated by a powerful arc lamp, and perhaps one or 
two rheostats, and you have a condition which makes good ven- 
tilation absolutely imperative. It must also be remembered, in 
this connection, that air taken in from the auditorium will 
be that which has arisen from the audience, and will therefore 
not only be the very warmest in the house, but also vitiated 
and rendered unfit for use by a human being. Moreover, if it is 
taken in entirely through the lens and observation ports an 
unpleasant draft is likely to be created, which blows directly 
in the operator's face. This latter may be stopped by install- 
ing glass in the ports (see "Glass in Ports" further on), but 
in that event other means of letting in air must be provided, 
and should be provided, whether glass is used or not. This 
is best done by making inlet openings near the bottom of 
the room, the same connected with the outer air at any con- 
venient point, thus supplying the room with fresh air instead 
of hot, foul air from the auditorium. But these latter openings 
should be provided with fire shutters which will close auto- 
matically in case of fire, in order to stop the draft. The heat 
of the room may also be largely reduced by connecting the 
top of the lamphouse to the operating room vent flue by 
means of a 3 or 4 inch metal pipe, having riveted joints. This 
pipe must be provided with a swing joint if the lamphouse 
must be shoved over to accommodate a stereopticon lens. 
This arrangement also operates to reduce condenser break- 
age by providing ample ventilation in the lamphouse. It is 
not costly to install, and will last indefinitely. Things of 
this kind add greatly to the comfort of the operator, and 
hence put him in better position to do his best work. The 
Massachusetts law contains the following provision concern- 
ing the ventilation of operating rooms, which is worthy of 
emulation : 

Operating rooms to be provided with an inlet in. each of the four 
sides, said inlets to be 15 inches long and 3 inches high, the lower side 
of the same not to be more than 2% inches above floor level. Said 
inlets to be covered on the inside by a wire net of not greater than 
%-inch mesh; netting to be firmly secured to the asbestos board by 
means of iron strips and screws. In addition to the above there shall 
be an inlet, in the middle of the bottom of the operating room, if pos- 
sible; otherwise in the side or rear of the operating room, not over 2% 
Inches from the floor. Said opening to be not less than 160 square 
inches area for a No. 1 operating room, 200 square inches area for a 
No. 2 operating room, and 280 square inches area for a No. 3 operating 
room; connected with the outside air through a galvanized Iron pipe 
with a pitch from the operating room downward to the outside wall 
of the building. The opening to be covered with a hood, so arranged 



as to keep out the storm, and the entrance to the operating room to be 
covered with a heavy grating over ^-inch wire mesh, if in wall; and 
arranged with damper hinged at the bottom, and rod or chain to hold 
said damper in any position. Mesh and gratings to be securely fast- 
ened in place, those in the walls to be bolted on as specified for the 
smaller inlets. 

Note: No. 1, No. 2 and No. 3 refer to the size of rooms. 

The same law contains a provision for a vent pipe not less 
than 12 inches in diameter from the ceiling of the operating 
room to the open air outside the building, or to a special in- 
combustible vent flue. In a two-machine operating room this 

pipe must be not les than 
16 inches in diameter and 
in a three-machine oper- 
ating room it must be not 
less than 18 inches in 

Glass in the Ports. 

Many operators are now 
using glass in both lens 
and observation ports, and 
this is a practice I can thor- 
oughly recommend, provided 
the glass for the lens port 
be carefully selected and 
quite thin. I think an old 
photographic plate would 
probably be ideal for the 
lens port, first, of course, 
cleaning the photographic 
emulsion off by washing 
with a strong solution of 
hot water and washing soda. 
I would strongly recommend 
that the observation port be 

surrounded by a shadow 1 box, 12 to 18 inches in depth, 
painted dead black on the inside. By shadow box I mean 
a casing such as you would have if you knocked the bottom 
out of a box and nailed what remained over the port. Where 
a box of this kind is not used there is more or less reflection 
from the surface of the glass, and, while operators say that 
after a few days' use they do not notice this, and that it 
does not interfere with their view of the screen, still I take 
the liberty of doubting the correctness of this statement. I 

Figure 91. 


believe they would be better able to see faint shadows on 
the screen with a shadow box surrounding the port, as per 
Fig. 91. 

Operating Room Equipment. Remembering that box office 
receipts of a moving picture theatre depend to a very great 
extent upon excellence of the results upon its screen, the 
wise manager will bend every energy toward the attain- 
ment of artistic projection, and will use every reasonable 
endeavor to enable his operator to produce high class, bril- 
liant, flickerless pictures, projected at proper speed to bring 
out and emphasize every good pointo and minimize any 
weak ones there may be. It goes without saying that there 
is small probability of continuous high class results coming 
from an ill-placed, small, poorly ventilated operating room, 
with inferior or worn-out equipment in charge of an oper- 
ator of mediocre ability. 

It also follows that the best results will be had from a rightly 
located, commodious, well ventilated operating room, equipped 
with up-to-date machinery and placed in charge of a thoroughly 
competent operator, who will keep the equipment in the best 
possible condition, the term '"competency" including industry 
and careful attention to detail, as well as knowledge. 

The mere possession of knowledge counts for little or noth- 
ing if its possessor is too lazy or shiftless to apply it in practice. 

In planning the operating room the architect should include 
two small clothes closets with substantial locks thereon, so the 
operator may have a place to keep his private belongings; 
also it is well to have two tool cabinets which may be locked 
up securely one for each operator. An operator should have 
a full equipment of tools, but it is rather discouraging to 
provide a costly kit of tools and then be compelled to leave 
them at the mercy of any one, from the janitor to the chance 
visitor, to say nothing of the other operator, who perhaps has 
none of his own, and, moreover, may not be inclined to take 
the best care of those belonging to others. There should be 
drawers, or a closet in which to keep supplies, such as car- 
bons, extra condensing lenses, etc., though, of course a shelf 
will serve, and if the walls be built of cement it is a compar- 
atively simple matter to provide cement shelves when the 
room is built. The supply closet may be built outside of 
the operating room if desired. There should also be 
plenty of hooks on which to hang wire, etc. It is an ex- 
ceedingly unprofitable thing to spend time hunting for a 
piece of wire or a tool, or some needed repair part, when 


something goes wrong. All these should not only be kept in 
stock but be kept in place, where the operator can find them 
instantly when they are needed. For instance: fuses should be 
kept near the fuse cabinet; when a fuse blows it is no time to 
be rummaging around through a miscellaneous lot of supplies 
to get a new one. If a wire burns in two, possibly stopping the 
show, it is no pleasant thing to have to look through a pile of 
miscellaneous tangled odds and ends of wire to find what you 
need. The point I am making is: Have a place for everything 
and everything in its place. This is not likely to be done, how- 
ever, unless proper shelves, hooks and closets be provided. 

// an operator does not keep things in order, being provided 
with proper places in which to keep them, then he is not the 
right sort of man to have in charge of an operating room. 

There should by all means be a wash basin, with running 
water, and a toilet either in or convenient to the operating 
room; both of these are quite essential, particularly where 
only one operator is employed. Often something will go 
wrong with the machine and the operator will get his hands 
covered with oil and dirt in making repairs. If there is no 
means of washing them, the next time he handles a piece of 
film there is likely to be considerable damage done. He is also 
very apt to soil everything he touches. From any and every 
point of view a wash basin ought to be installed in or near the 
operating room, and a toilet should be required by law, since in 
many cases the operator is literally chained right there in the 
operating room for hours at a stretch. 

An one end of the operating room there may be a rewind- 
ing room, the two separated by a fire-proof walland door, the 
shutter master-cord passing through this wall and down over 
the rewinding table, with a fusible link, as already set forth. 
If there is a motor or generator set, or a mercury arc rectifier, 
there should be a separate room provided for them at one end 
of the operating room. These machines should not be placed 
in the room where the film is rewound, and a mercury arc 
rectifier should never be placed in the operating room itself, 
because it makes the room too light, and it is thus made diffi- 
cult for the operator to discern faint shadows on the screen. 

Supplies for the Operating Room. I cannot imagine a 
more foolish and utterly mistaken policy on the part of a 
manager than to be niggardly in the matter of projection 
room supplies. On the other hand I by no manner of means 
approve of the operator wasting supplies or being extrava- 
gant with them. 


I take the position that an operator who cannot be trusted to 
be careful and economical with supplies when he has plenty is 
not a fit man to be in charge of an operating room. 

However, in this connection it must be remembered that 

A good, competent operator, who understands his business 
and is allowed to do things as they should be done, does not 
wait until a part breaks down entirely, thus perhaps stopping 
the show until repairs are made; he renews worn parts before 
the break comes. 

It is false economy, from any point of view, to try to get 
the last particle of wear out of operating room equipment. 
Take, for instance, asbestos wire lamp leads. Altogether too 
many operators use their lamp leads, particularly that por- 
tion inside the lamphouse, too long. Inside the lamp- 
house the wires are subjected to increasing heat from the 
arc as they approach nearer to it, and as the temperature 
of metal rises its resistance also rises. Copper oxidizes 
under the action of heat, and where a wire is worked close 
to its capacity electrically, and you add a high temperature 
of heat from an outside source, the effect is to raise the re- 
sistance of the wire, thus lowering its carrying capacity and 
setting up still more heat and rapid oxidization and deterio- 
ration. In a very short time the strands turn brown, then 
dark brown, and presently if you bend the wire near the 
lamp binding post, you will find it has no "spring"; it is like 
a piece of string. Under this condition its resistance is very 
high and it is consuming wattage which in a few hours' time 
will more than equal the cost of the 1 wire. If you strip the 
asbestos back you will probably find its strands have turned 
brown for a considerable distance. ' 

I would recommend that where No. 6 asbestos stranded 
lamp leads are used they be cut off and that a good, heavy wire 
connector, D, Fig. 30, be attached and then connection made 
from that to the lamp with a short piece of the same wire. 
Then where, say, 40 amperes are used, once every week re- 
move this short piece of wire, throw it away and substitute 
a new piece. This will cost you a little more than twenty 
cents, but it will save that much or more in current, besides 
giving a better light. Where less than 40 amperes are used 
the wire can be continued in use for a somewhat longer time. 
When the amperage is very high, larger wire, or No. 6 
doubled, should be used inside the lamphouse. 

There is always tendency to use the intermittent sprocket 
of the projection machine too long. Intermittent sprockets 


of modern projectors are very carefully made and hardened, 
but, notwithstanding this fact, in the course of time the con- 
stant wear of the film will cut a notch in the side of the 
sprocket teeth and in time wear them into a hook shape, 
which has tendency to produce unsteadiness in the picture, 
as well as do serious injury to the film itself. Therefore, this 
being the fact, it would be true economy to replace the in- 
termittent sprocket before the teeth show any appreciable 
wear when subjected to examination, using a condenser lens 
as a magnifying glass. 

I mention these two examples merely as typical, and place 
them in evidence as showing that it does not pay to be too 
economical in the matter of operating room supplies; also 
as proof that lack of knowledge often causes a manager to 
practice what is in effect false economy, or, in other words, 
practice economy which is, as a matter of fact, exactly the 
opposite. It never pays to compel the operator to use worn 
parts, since worn parts always tend to injure results on the 

Managers would do exceedingly well to secure an operator in 
whose judgment they have confidence, and, having done so, 
alloiv him reasonably free hand in the matter of supplies. 

It is an absolute fact that failure to grasp this simple idea, 
and apply it in practice, is causing the moving picture industry 
many, many thousands of dollars every year through loss of 
business. Tens of thousands of people would be more regular 
patrons of moving picture theatres if the pictures in those 
houses were placed on the screen in the best possible manner, 
but placing the picture on the screen in the best possible man- 
ner is utterly impossible to the operator ivho is not supplied 
with proper equipment or with needed repair parts. 

In the operating room should be an ample supply of car- 
bons, wire of the various kinds used, plenty of fuses of the 
different sizes and kinds used, slide cover glasses (clean, 
not dirty), stereopticon mats and gummed binder strips, 
extra parts for the intermittent movement, and, if it be a 
Power, Motiograph or Simplex machine, then an entire intermit- 
tent movement, including the framing carriage, already assembled 
and ready to slide into place in the machine; extra machine 
bushings for intermittent and cam shaft bearings, extra con- 
densers, and, in fact, everything likely to be needed. 

In the room should be some sort of a water-tight, metal 
receptacle of such form that it will not be easily upset, this 
to be kept half full of water to receive hot carbon butts. If 
the operating floor is covered with iron (bad practice, but 


still followed in some localities) it should be covered with 
insulating material, such as cork matting, rubber matting or 
linoleum, or at least there should be an insulating mat of 
ample size on the operating side of both machines and the 
stereopticon, otherwise the operator is most likely to be 
subjected to unpleasant shocks, though this does not hold 
true if the thoroughly and effectively grounded 
to the floor. 

Operator's Chair. Some managers insist upon the oper- 
ator standing up, and will not allow a chair in the room. 
With all due respect to them, that is pure, unadulterated 
nonsense. Some men prefer to stand up, but to other men 
standing several hours continuously on their feet is a tre- 
mendous hardship. The writer, for instance, could not 
and would not do it. At the end of two hours he would be 
too badly exhausted to do good work. Anyhow, there is no 
earthly reason why the operator should not be seated com- 
fortably at his machine. If the observation port be properly 
made, so that he can view his picture from that position, 
there is absolutely no reason whatever to suppose he won't 
do just as good work seated as Wihen standing up. 

As a matter of fact the operator is very likely to do better 
work when seated than when standing, because when standing 
there is always the temptation to move around, whereas if 
seated at the machine he is likely to remain right there in front 
of the observation port where he ought to be, and where he 
must be to deliver the best results. It is therefore good policy 
not only to allow the operator to be seated at the machine, but 
to provide a comfortable chair, or at least a stool of proper 

Ammeter and Voltmeter in the Operating Room. It is, m 

the judgment of the author, an exceedingly good investment 
to locate an ammeter or voltmeter, particularly the former, 
in such position that it will be constantly in front of the 
operator when he is in operating position at the machine, 
the same to be connected to the operating room feeders, so 
as to indicate all current used in the room.. 

There is a certain point at which the projection arc will 
produce maximum illumination with a minimum current 
consumption. Just a little movement of the carbons away from 
this position will jump the current consumption by anywhere 
from 5 to 20 per cent., without in any way increasing the light 
brilliancy in fact it is likely to decrease it. With an am- 


meter placed directly in front of the operator he is able to, 
and, if a careful man, will maintain his arc at the point of 
maximum brilliancy with minimum current consumption. I 
believe that, in the average theatre, an operating room 
ammeter, if properly located, will pay for itself in a very 
short time. A good ammeter may be had at from twelve to 
fifteen dollars. 

The method of connecting an ammeter or voltmeter is set 
forth in Fig. 92. 

Figure 92. 

Anchoring the Machine. It is absolutely essential to 
steadiness! of the picture on the screen that the machine 
itself be rigid, and without the least vibration. Most modern 
projectors have tables or pedestals sufficiently solid to re- 
quire no additional anchoring, provided the floor itself be 
without vibration. However, there are still a number of old 
style tables in use, and, for the benefit of the users thereof, 
I illustrate an excellent table anchor in Fig. 93. 

In Fig. 93, A is a piece of 1^4-inch pipe, at the top of 
which is a flange with a right-hand thread and at the bot- 
tom a flange with a left-hand thread. Pipe A is cut just 
long enough barely to clear the floor and ceiling when the 
flanges are not on.. Now screw the flange on and with a 
Stillson wrench turn the pipe counter clockwise, which will 
have the effect of forcing the top flange against the ceiling 
and the bottom flange against the floor, thus firmly anchor- 
ing pipe A, to which the machine table is then attached by 
means of part B. The front of the table may then be 
anchored to the front wall as shown. Legs of tables of the 
tvpe shown in Fig. 93 should be set in iron sockets, or, in 
rneir absence, be placed in an indentation made in the floor. 



These tables are, however, out of date, and are rapidly being 

Tools. The operator should, as has been remarked, be in 
possession of a kit of tools enabling him to do ordinary re- 
pair jobs. Such a kit of tools cost several dollars, but it is 
a good investment. The manager is likely to have more 
respect for the operator who owns a good tool kit than for 
the one who shows up with a ten-cent screw-driver in one 

,~L shaped piece to 

y front end 
fable' to froni 
H of bootk 

figure 93. 

pocket and a pair of broken pliers in another. In the second 
edition of the Handbook I gave a list of tools, to which I 
see no reason for either subtracting or adding, except in 
the item of a small hand-bellows, which is a very convenient 
tool with which to blow dust and dirt from around switches, 
and from around the pole-pieces, armature and places where 
a brush cannot be used on a motor or generator. This is a 
thing, however, which does not really belong to the operator's 
kit, but should be supplied by the manager, and should have 
a place in every operating room. It is a necessity where a 


motor generator set is used. The following is the list of 

One pair "button" pliers 8 or 10 inch; one pair 8 or 10 inch 
lineman's side cutting pliers (I leave the matter of size open, 
as some prefer one and some the other); one pair 8 or 10 
inch gas pliers; one large and one medium screw-driver; one 
screw-driver with good length of carefully tempered blade 
for small machine screws, to be heavily magnetized so as to 
jhold small screws; one pair of pliers for notching film, see 
Fig. 76; one small riveting hammer; one claw hammer; one 
small cold chisel; one medium-sized punch; one very small 
punch for star and cam pins; one small pair tinner's snips; 
pair blunt-nose film shears (such as clerks use); one small 
gasoline torch for soldering wire joints; one :hack-saw. With 
this kit you will be able to do almost any ordinary job, but 
you will have use for them all. In addition to the above the 
house manager should furnish one 8 and one 10 inch flat file, 
one $/% round file, one 8 inch "rat tail" file, a small benc'h 
vise with anvil and some soldering flux and solder wire. 

In this list there is nothing which will not be found of use, 
and many operators will desire and acquire a more elaborate 

Tools in Order. It is of the utmost importance that the 
operator's tools, be they many or few, be kept in order, 
neatly arranged on the wall, the screw-drivers and pliers 
within handy reach from operating position. One of the 
most reprehensible habits possible is that of dropping tools 
when one has. finished using them and letting them lie until 
needed again. 

It would be hard to estimate how many thousands of times 
moving picture theatre audiences have sat in the dark, wait- 
ing patiently while an operator searched around looking for 
the pliers, screw-driver, or other tool needed to make a repair, 
which he had thrown down wherever he happened to use it 
last. Often I have gone into operating rooms and found the 
operator's tools lying on the floor in a jumbled pile under- 
neath the machine. This kind of thing is not only exceed- 
ingly unworkmanlike but decidedly sloppy. The man who 
does things that way is never likely to make any large suc- 
cess, either of operating or anything else. 

My advice to the operator is~ have a good kit of tools and 
keep them neatly arranged and in perfect order. 


My advice to ihc manager is to discharge the operator who 
is satisfied to own a pair of pliers and a screw-driver, or who, 
having other tools, does not keep them in order. If he is un- 
workmanlike in so important an item, it is likely he will be un- 
workmanlike in other things zvhich zvill reflect directly on the 
screen in the shape of faulty projection. 

Announcement Slides. It is frequently necessary to make 
announcements to the audience. There are a great many 
different ways in which very good appearing slides can be 
hastily prepared. There are inks on the market, in several 
colors, with which one may write, using an ^ordinary pen, on 
clean, plain glass, just the same as he could write on paper. 
There are also a number of slide coatings for sale on which 
writing may be done with a sharp pointed instrument. 
These slide coatings are particularly to be desired for any 
slide which must be made on the spur of the moment, by 
reason of the fact that a number of them can be got ready 
and laid tip on a shelf in a pile where they will keep in- 
definitely. If anything happens and you wish to say some- 
thing to the audience, the operator can write on these slides 
with anything having a sharp point. For instance, sup- 
pose something occurs that will cause a delay of two min- 
utes. Within five seconds the operator can write on one of 
these slides ".Unavoidable Delay of Two Minutes," stick it 
in the stereopticon and project it to the screen. The audi- 
ence will then be satisfied to wait for that length of time. 
I only suggest this as one possible way in which slides of 
this kind may be utilized. They should be kept in the oper- 
ating room ready for instant use. Please understand in 
this I am not referring to program slides which the man- 
ager himself will wish to prepare, but merely those designed 
to be used for emergencies. 


The wiring of the operating room is a matter which should 
be carefully planned before the construction of the room is 
begun, particularly if the walls are to be of concrete or 

The operating room feeders must be large enough to 
carry the entire load of the operating room. That is to say, 
if there are, for instance, two projection arc lamps, a dis- 
solving stereo, a spot light and four incandescent lamps, then 
the operating room feed wires must be large enough to carry 


the combined amperage of all these lamps when they are all 
burning. True, they probably never will be burning all at 
one time, but that does not alter the fact that the wires must 
be able to supply them all without overload. 

Note. When A. C. circuits are run in conduit always place 
both wires of the circuit in the same conduit. If they be run in 
separate conduits a highly objectionable inductive effect will 
be set up in the conduit. 

In order to figure the necessary amperage capacity, pro- 
ceed as follows: First estimate the combined amperage. 
Suppose there are two projectors and you propose to use 40 
amperes from .a HO volt line through resistance. This would 
call for 40 + 40 = 80 amperes at the two projector arcs. 
Suppose there is a dissolving stereo which requires 15 am- 
peres per light, or a total of 30 amperes, a spot light taking 
15 amperes and incandescent taking 5 amperes; thus 
gO-|-30-f 15 + 5 = 130 amperes. Turning to Table 1, Page 
42, we find that if the feeders be two wire, it will require 
00 R. C. wire to carry that amount of current. 

If, however, the feeders are three wire, then, since when 
the lamps were all burning the arc would burn in series on 
220 instead of 110 (See three-wire system, Page 56), the am- 
perage requirement would be cut in half and it would only 
be necessary to have No. 5 feeders. 

Again, if all the lamps are to be operated from a motor 
generator set, rotary converter, mercury arc rectifier, or on 
current taken through an economizer (transformer), then 
the operating room feeders need only be large enough to 
supply the primary capacity of these devices, or the com- 
bined amperage of the arcs reduced from secondary to 
primary, provided this apparatus be in the operating room. 

The operating room feeders should be brought in at the 
most convenient point, through conduits, and carried to a 
metal switchboard cabinet. As has been already set forth 
under title "Operating Room," the circuit conduits should be 
laid before the room is built, and be built into the wall, floor 
and ceiling. There is no sense in having the operator stum- 
bling over a conduit laid on the floor; also, a conduit laid on 
wall and ceiling looks unworkmanlike. It looks like a "half 
baked" job. Do the thing right and embed the conduit in 
the wall when building the room, carefully planning the out- 

The main operating room switchboard cabinet should con- 
tain (a) main feeder switch A, and fuses B, Fig. 94, 


Figure 94. 


carrying the entire operating room load; (b) a small switch 
and fuses, C, Fig. 94, carrying the operating room incan- 
descent circuits; (c) cutout blocks D, E, F (as many as 
needed), carrying fuses for the various circuits, and, if de- 
sired, switches also. In the drawing, Fig. 94, we will 
assume circuits 1 and 2 to supply the projection machine 
arcs, circuit 3 and 4 the dissolving stereo, circuit 5 the spot 
light, and circuit 6 the incandescents. 

The switchboard plan shown in Fig. 94 is merely illus- 
trative. The board may be built up to accommodate as many 
or as few circuits as may be necessary. The cutout blocks 
shown may be porcelain base cutouts with switches, similar 
to those illustrated in Fig. 18, Page 72; they may be 
porcelain base cutout blocks without a switch, as shown, or 
they may be slate base switches with fuse receptacles. 

Where the three-wire system is used to feed the operating 
room and connection is made to the neutral, the projection 
arcs should be connected on opposite sides. It is, of course, 
impossible to balance the operating room load on a three- 
wire system because ordinarily only one projection arc will 
be burning at a time, but suppose you connect both lamps 
of your dissolver to one side, then when the dissolver is in 
use, instead of the load being balanced there is approxi- 
mately 30 amperes on one side and nothing on the other, 
which is bad. Then, too, if both projection lamps are con- 
nected to one side, when the arc of the idle machine is struck 
to heat the carbons, before switching over to a new reel, for 
a short time the entire load of both projectors is on one side, 
meaning that anywhere from 60, 80, 90 or even 100 amperes 
of current would be on one side, and this much of an un- 
balanced effect would be felt by a good sized power plant. 
To sum this matter up: 

Where a three-wire system is used to feed the operating room, 
connect projection arcs to opposite sides and connect dissolver 
lamps to opposite sides, except where mercury arc rectifiers, 
motor generators or economizers are used, in which case it 
is much better to leave the neutral idle and connect only to 
the outside wires, purchasing your motor generator or econo- 
mizer with that end in view with a 220 volt motor. Mer- 
cury arc rectifiers may be used for either 110 or 220. 

The location of the operating room switchboard cabinet 
will necessarily be determined by local conditions, but use 
care to place it conveniently. 


There is nothing to be gained by making things inconvenient 
for the operator, and there is much to be lost by doing so. 

As to the main operating room fuses, I would suggest 
they be placed as s'hown in Fig. 94, rather than on the other 
side of the switch. Inasmuch as the operating room feed 
wires, including the operating room main switch, is pro- 
tected by fuses on the main switchboard, there is no neces- 
sity for protecting it further, and it is more convenient to 
install fuses at B if the fuse block is "dead" than if it be 

In some cities the power company, will not allow the neu- 
tral of a three-wire system to be run to the operating room. 
This compels the use of 220 volts which, if rheostats are 
used, is very wasteful indeed. The reason for this is the 
heavy unbalancing effect (already explained) of the projec- 
tion arcs. It is quite possible that this unbalancing effect 
might, be very serious, from a power company's point of 
view, particularly in a small city where there are a number 
of moving picture theatres and the power company's genera- 
tors likely to be pretty heavily loaded. Supposing, for in- 
stance, one side of a street main supplies five moving picture 
theatres, each having two machines connected to the same 
side of a three-wire system. Now suppose it happens, as it 
might easily happen, that the operators in all five theatres 
chanced to be changing from one machine to the other at 
the same time, and all struck the arcs of their idle machines 
at the same moment. This would mean, assuming that all 
were pulling 40 amperes at each arc, a total unbalance of 400 
amperes (five theatres, two arcs to the theatre), which would 
probably put everything else attached to this same generator 
out of business, at least temporarily. 

Even if these five theatres each had their two arcs on 
opposite sides, when only one arc was burning it would mean 
an unbalance load of 40 X 5 = 200 amperes, so you see the 
light company is perfectly justified in demanding that only 
the outside wires be used. But this does not hold good if cur- 
rent is taken through resistance. In that event the changing to 
the two outside wires would have no effect at all, except to 
load both generators of the system that much more heavily. 
Instead of having one generator pulling an unbalanced load 
of 400 amperes, as before set forth, if connected to the 
two outside wires through resistance both generators would 
be pulling a load equal to 400 amperes at 110 volts, when 
all arcs were burning, therefore the only thing gained is a 



big additional (double) and entirely useless waste of elec- 
trical energy. 

What the light company has the undoubted right to do 
is to demand that the projection lamps of the theatre be 
connected to opposite sides of a three-wire system when 

Figure 95. 

current is taken through rheostats, and if an economizer, 
motor generator, rotary converter or mercury arc rectifier 
be used that the supply be taken from the outside wires. 

In Fig. 95, the typical, and in some ways excellent operat- 
ing room of the Park Theatre, Bangor, Me., is illustrated. 
It will be observed that the projection machine circuits are 
led under the floor and up to an outlet immediately under 


the lamphouse, which is exactly as it should be. The vent 
flue seems to be of ample size and well located. The 
switchboard is apparently neatly put together, but should 
have a metal cabinet to protect it. The switch and volt- 
meter and ammeter near the ceiling at the right govern a 
5 k.w. motor generator set. 

The work bench is made of wood, which would be ob- 
jected to in many cities, though the objection has no real 
basis. There is about ;as much danger in a wooden work 
bench in an operating room as there is in a pile of sawdust 
in an ice house. The fuse links of the shutter cord are 
so located that they would be of slight value in case of fire. 
There is no evidence of toilet conveniences, though it is 
possible they may be placed near-by but outside the op- 
erating room. The tools would look better in a neat rack 
over the work bench, instead of lying on the bench. 

In Fig. 96, Fig. 97, and Fig. 98, we see three views 
of a most excellent operating room installation at the 
Monarch Theatre, Cleveland, Ohio. In this installation 
there is little to criticise. The fire shutters are hung from 
a master-cord, which is correct practice. As shown the 
master-cord fuses are wrongly placed, but I am informed 
that since the picture was taken the fuses have been car- 
ried down under the magazine and placed over the machine 
apertures on brackets. What tools are in sight are neatly 
hung up on the wall. The conduit is not buried in the 
floor, ceiling or walls as it should be, but this could not 
be avoided as the walls of the room are of hollow tile and 
the local laws will not permit a conduit to be placed inside 
of that kind of operating room wall. It is true that a 
conduit on the face of the wall serves the purpose just as 
well from an electrical standpoint as it would were it 
buriedi in the wall, but it looks bad and spoils the finish 
of the room. There is a wash basin, with cold and hot 
water, but an apparent absence of seats for the operators, 
and that I cannot agree with. 

/ believe the operator is much more likely to remain at his 
machine, where he belongs, if there is a comfortable seat pro- 
vided, and surely he will do as good or better work when 
seated at his machine than when running around the operating 
room, letting George (the motor) project the picture. 

The room is 10 x 15 feet, with a ceiling 10 feet at the 
walls and 12 feet in the center where there is a 36 x 40 inch 
vent flue, in which is an 18-inch G. E. exhaust fan. In the 
rear wall, only part of which is shown, are two windows 






30 x 40 inches, each having a 16-inch fan set in its center. 
The windows open on a 10-foot court, and are metal instead 
of glass. 

Each machine is connected to two rheostats in multiple, 
and it will be noted the rheostats are placed near the ceil- 
ing, where they should be. There is a voltmeter and an 
ammeter, but these two instruments are poorly located, 
as the operator, when standing ,at the machine, would have 
to turn round to see them, and that is not good. There 
are three projectors, which eliminate all possibility of 

Figure 98. 

trouble * from a break-down. The observation ports are 
8x12 inches. The walls are of tile and brick, 18 inches thick, 
with a ceiling of steel roofing with an air gap of 3 inches 
above and then metal lath plastered. The floor is of 
cement, built up on the ground, covered with battleship 
linoleum one-fourth-inch thick. The floor of the operating 
room is only 3 feet 6 inches above the main floor of the 
theatre. The lens ports are 6 feet 8 inches from the main 
floor, which places the lens in almost perfect line with the 
center point of the screen. The cabinet next to the sink 
contains controls for the heating system, the center one the 
switches for the theatre lights, and the third the fuse board 



for the operating room. There are two sets of No. 6 wire 
running to each machine, each set connected to separate 
fuses. The machine switch of the two outside machines is 
double-throw, so that by throwing the switch over a new 
set of fuses is cut in. We see the corner opposite the sink 
in Fig. 98. The bank of six lamps and the batteries are 
the business end of the safety lighting system required by 
Ohio law. It automatically lights small, low voltage lamps 
in the auditorium if anything goes wrong with the main 

Figure 99. 

circuit, thus preventing the plunging of the auditorium into 

I am informed that the card index shown immediately 
under the cabinet contains more than two thousand ques- 
tions and answers on operating and the things allied thereto. 
The typewriter is used in connection with the card index. 
Notice the extra parts neatly arranged on the wall; the 
program slate; the extra reels and wire; the oil cans and 
the electric battery flash lamp. 

This installation is the work of Howard W. Codding, 
who, by the way, was one of the organizers of the Cleve- 
land operators' union. Judging from these pictures, Brother 
Codding is a thoroughly capable, enterprising and progres- 
sive operator, and one not merely satisfied to be able to 


draw his Saturday night's pay, giving the least possible 
mental and physical effort in return. 

Later: I am informed that there are comfortable chairs 
for the operators, though they do not show in the pictures. 

Fig. 99 shows the operating room of the Pathe projec- 
tion room at the American headquarters of that company. 

I have used these operating room illustrations for two 
reasons: first, they are excellent of their kind, and I believe 
will serve to offer suggestions to others planning similar 
installation; second, to mildly criticise the faults shown, 
but I wish it understood that these installations are never- 
theless good, and good ones to copy, too, with the faults 
mentioned eliminated. 

With regard to the projection circuit, when it cannot be 
carried under the floor it should by all means be carried 
through and above the ceiling, if possible, or if that cannot 
be done then along the surface of the ceiling to a point 
just to the left of the projector lens hole, and thence down 
the wall and back, either along the left side of the machine 
or along the floor, according to individual preference, to 
an outlet located under the lamphouse. Some of these 
various methods are shown in the illustrations. There is 
no rule which can be made to apply to all installations. 

As a rule inspectors require that all switches, except those 
of the inclosed type, and all fuses be inclosed in a metal 
cabinet, and it undoubtedly does add .an element of safety, 
since there is always a chance of something inflammable 
falling against an open switchboard and causing trouble, or 
of the operator himself accidentally coming into contact with 
it and receiving a bad shock or burn. 

With modern projectors the operating switch is invariably 
a part of the machine, and located under or beside and 
below the lamphouse. These switches must be of the 
inclosed type inclosed in a sheet metal casing. 

Double Throw Connection. Two projectors should never 
be connected through a double-throw switch with the supply 
attached to the center contacts, so that it is necessary to ex- 
tinguish one lamp to light the other', except in cases where 
current is taken through a single motor generator or recti- 
fier of insufficient capacity to supply both lamps. In that 
event it is well to make that sort of connection, but, on 
the other hand, it is advisable where that condition prevails 
to arrange so that the idle lamp may be operated through 
a rheostat taking current directly from the supply lines 



ahead (on the street side) of the motor generator or 

This sort of connection, shown in Fig. 100, is entirely 
practical and not at all expensive to make. In practice I 
think the change from rheostat to compensarc could be 
made without breaking the arc. The idle lamp would be lit 
up, using current through the rheostat, about two or three 
minutes before the reel on the other machine was ended 
and at the changeover the operator would quickly throw 

Figure 100. 

over the four-pole switch and pull the machine table switch 
on the machine which had finished its task. 

Except under the circumstances just named every machine 
circuit should be entirely independent of every other circuit. 
Connect every projector lamp and every stereo lamp entirely 
independent of every other lamp and you will avoid trouble 
and annoyance. 

Polarity Changer. Where the supply is taken from a 
small D. C. plant it sometimes occurs that when dynamos 
are changed the polarity changes, which requires the instant 
switching of your own wires to bring the positive back to 



the top carbon. This may quickly be accomplished by the 
installation of a double-throw double-pole switch, such as 
is seen in Fig. 101. Throwing this switch over changes 
the polarity of the wires. The cross wires should be pro- 

Figure 101. 

tected by flexible insulating tubing in addition to their own 

Fig. 102 is a diagram of a combined polarity switch and 
fuse changer. By throwing switch A a new set of fuses 

Figure 102. 

is cut in and by throwing switch B the polarity at the arc 
is changed. 

Connecting to Two Sources of Supply. For various rea- 
sons it is frequently desirable to make connection to two 
separate sources of electrical supply. One may have one's 



own light plant, but wish, in case of accident, to be able to 
instantly connect to the wires of the city plant. This may 
readily be done, but due to varying conditions details may 
vary widely in different cases. Suppose we have a house 
plant delivering direct current at 110 volts, while the city 
plant produces A. C. at 110 volts; both systems two-wire. 
The problem then is simple. 

Install a double-pole, double-throw switch, as per Fig. 103. 
The house plant being D. C., we shall not need nearly so 
much amperage from it as would be necessary for equal 
screen illumination with the city plant, A. C.; therefore, we 
install two rheostats, A and C, the lower one, A, to be used 
with a D. C. house plant. B is a double-pole single-throw 

Figure 103. 

knife switch which is open when D. C. is in use, so as to 
use only rheostat A. When we throw over to the A. C, 
however, we close switch B, thus cutting rheostat C in 
multiple with rheostat A. Rheostat C should have capacity 
sufficient to build the combined amperage of the two up 
to that necessary for good illumination of the screen. Sup- 
pose we use 35 amperes D. C. In order to secure anything 
like the same curtain brilliancy rheostat C must have ca- 
pacity sufficient to deliver 25 amperes which, combined with 
the capacity of rheostat A, will give 60 amperes at the arc. 
But we must remember that, owing to the shorter A. C. 
arc, hence the less arc resistance, rheostat A will deliver 
somewhat more current on A. C. than it will on D. C., the 
voltage of the supply being the same in both cases. We 



will probably, therefore, be not far out of the way if we 
have rheostat C of capacity to deliver 20 amperes at the arc. 
We may, however, instead of this, install a transformer 
(economizer, inductor, compensarc, etc.), in place of rheostat 
C, Fig. 103, and with a triple-pole double-throw switch, wired 
as per Fig. 104, cut out resistance A, Fig. 103, substituting 
the economizer therefor. Merely throwing the switch over 

Figure 104. 

would then change from rheostat to transformer, and vice 
versa, though the transformer would be "alive" in the sense 
that you could get a shock from it. But this would do no 
harm. If you wish to "kill" the transformer entirely when 

Figure 105. 

using the rheostat, it may be done by installing a S. P. S. T. 
switch at X, Fig. 104. 

Please understand there are many other switch arrange- 
ments possible. Such things may be done in many ways. 
Those suggested merely illustrate two possible methods. 
Another and still better way to cut the two rheostats in 


multiple, Fig. 105, is by means of a triple-pole, double-throw 

A careful tracing out of the connections in Fig. 105 will 
show that when the switch is thrown to the A. C. supply 
side the two rheostats are in multiple, while when the D. C. 
side is in use only rheostat 1 is working. Should the supply 
voltage be higher on one system than on the other, a higher 
voltage rheostat could be substituted for A, Fig. 103, and 
rheostat C be made of such capacity that it will bring the 
amperage up to normal when on the lower voltage. 


ONE of the most puzzling things to the novice, and one 
not too well understood by many experienced opera- 
tors, is what is termed a "ground," meaning a con- 
tact with some current carrying material by means of which 
the current can escape from one wire of a circuit into the 
ground and through the ground to some point where a wire 
of opposite polarity attached to the same generator has con- 
tact with the ground, or is "grounded." Incidentally, when 
a conductor of current, such, for instance, as the metal of 
a lamphouse, has electrical connection with either side of 
the circuit, that side of the circuit is said to be "grounded 
to the lamphouse," e\en though the lamphouse itself is insu- 
lated from the opposite polarity, so that no current can 
flow. This is, however, not a ground in the true sense. 

The neutral of all Edison -three-wire systems is grounded 
to earth. This is a true ground, and if an accidental ground 
occurs on the other wires of the system, the current will 
return to the dynamo through the earth, and thus form a 
short circuit, blowing the fuses protecting the circuit on 
which the ground occurs. 

And now right here let me make it clear that the somezvhat 
common belief that current seeks to escape from the wires 
into the ground is wrong, except ivhen by so doing it can find 
a path to a ivire of opposite polarity which is attached to the 
same dynamo. Let me also emphasize the fact that the cur- 
rent generated by one dynamo will not seek the opposite 
polarity of another dynamo, but only that of its own gen- 

Electric current has absolutely no affinity whatever for any- 
thing under the sun except a wire of opposite polarity attached 
to the same generator. 



If the positive or negative wires of a generator carrying 
ten thousand Volts, or for that matter fifty thousand, were 
thoroughly and completely insulated (a condition never 
found in actual practice) you could stand with your bare 
feet on wet ground and 'handle a wire carrying the full 
voltage with your bare hands without any danger whatever, 
but if you attempted to do this and the wire of opposite 
polarity be grounded at any point, the current would in- 
stantly leap through your body into the earth, follow the 
path of least resistance to the point where the other wire 
was grounded, and enter it; or, lest we become confused, 
assuming that current flows from positive to negative, if you 
held the negative wire, then the current would leave the 




. (- 


Figure 106. 

positive, enter the ground, pass through the ground to your 
feet, up through your body and into the negative. The 
effect, insofar as shock be concerned, would, of course, 
be identical, regardless of which way the current might 
flow. I emphasize this because some are puzzled by the 
fact that when they touch a negative wire they get just as 
heavy a shock as they do when they touch the positive. 

Examining Fig. 106, A is a circuit attached to dynamo 
G, and B a subsidiary circuit branching from it. Now, let 
us assume that the system is grounded at point Z, in the 
lower or negative carbon arm, and at point X on the posi- 
tive of the subsidiary circuit. In this case the current would 
leave the positive at X, travel through the ground, seeking 
the path of least resistance, which might lead it through 
some distance, to point Z, where it would enter the carbon 



arm. You will observe that it does not enter circuit C, 
attached to generator Y, although the negative of that 
dynamo is grounded, let us assume, at T. The curves in 
the line are merely designed to show the devious path the 
current may traverse in seeking the path of least resistance. 

Again, let us suppose rheostat E to be grounded, it being 
on the true positive of an Edison three-wire system, or 
the positive of an insulated system, and that a ground on 
the neutral or the negative exists at O. The current then 
leaves your rheostat, passes into the earth and follows a 
water main, or possibly a gas main, or perhaps the earth 
itself to point O, where it finds what it is seeking, viz.: a 
point at which it can get into the negative wire.. 

With regard to the three-wire system grounding, it is a 
great puzzle to many. Let me say, in the beginning, that 
there are two kinds of three-wire systems, viz: the Edison 
system, in which the neutral is always thoroughly grounded 
at the generator and at other points, and the three-wire 
system in which the whole system is insulated. The reason 
for grounding the neutral in the Edison system is to prevent 
any possibility of the conduit in buildings being charged at 
220 volts, or, to put it in electrical terms, to limit, the dif- 
ference of potential between any wire and the conduit sys- 
tem in buildings to 110 volts. The insulated three-wire 
system is, so far as the writer knows, only used for small 


Figure 107. 

With the Edison three-wire system your test lamp will 
not show a light from ground to neutral, and if your neutral 
carbon arm should be grounded there will be no effect, 
unless the rheostat is in the neutral wire, in which case the 



fuses may blow when the arc is struck, by reason of the 
fact that the striking of the arc completes the circuit through 
the ground, as indicated in Fig. 106, thus eliminating a por- 
tion or all of the rheostatic resistance, the amount elimi- 
nated depending upon how heavy the ground may be. 

It might incidentally be mentioned that, theoretically at 
least, it would be quite possible when using the Edison 
three-wire system to locate the rheostat on the outside wire, 
remove the insulation from the carbon arm of the lamp to 
which the neutral is attached, disconnect it from the wire 
and thoroughly ground the carbon arm, whereupon the arc 
would operate the same as though it was connected up to 
the system. The above is merely cited as a curiosity, and 
not because it is really a practical thing to do. 

Gounds may be tested for with a test lamp. This may be 
a single lamp, of the voltage of your system, to which two 
wires of convenient length are connected, or when using 
the Edison three-wire system, the test lamp may be made up 
as per Fig. 107. The lamp combination used in Fig. 107 is 
designed to be used on either 110 or 220 volts. 

Figure 108. 

On 110 volts, wires A and C only should be used, but on 
220 use wires A and B, the lamps being 110 volt globes, 
preferably of low candle power, though standard lamps will 
do. If you are not using 110 or 220 volts, then you will, of 


course, use lamps of whatever voltage your system may 
happen to be. 

It is highly desirable to have a permanent, known ground 
in the operating room, and this may best be established by 
either attaching a copper wire, No. 22 or larger, to a water 
pipe, or else by soldering the end of such a wire to a copper 
plate not less than one foot square, and burying the plate, 
embedded in powdered coke, in the ground deep enough 
to secure its contact with moist earth. Having established 
the ground by either of the above described methods, carry 
the other end of the wire through the wall of the operating 
room at any convenient point and attach a binding post at 
its end. This forms a permanent, known ground. To at- 
tach the ground wire to the water pipe the best method is, 
using a file or emery cloth, to polish the pipe perfectly 
clean and bright for one or two inches of its length, and 
then, first having stripped the insulation from four or five 
feet of the end of the wire, and scraped the wire perfectly 
clean, wrap the same many times around the pipe tightly, 
and fasten it securely in place, but be sure that the wire is 
held tightly to the pipe. Having finished this, we will pro- 
ceed to attach the test lamp socket firmly to the wall, in any 
convenient manner, close to the end of the ground wire, and 
join one of its binding posts thereto by means of a short 
piece of wire. Now cut a piece of insulated wire (braided 
lamp cord is excellent for the purpose) long enough to reach 
from the other binding post of the test lamp to any point in 
the operating room where you are likely to want to make a 
test. Attach one end of this wire to the other test lamp 
binding post and you will then be in a position to make a 
ground test instantly at any time, simply by touching the 
lead wire from the lamp to the object you desire to test, the 
lead wire being, of course, kept coiled up on the wall beside 
the test lamp when not in use, all of which is shown in 
Fig. 108. 

It is quite possible the object to be tested may be grounded 
and still not light the lamp, by the reason of the high resist- 
ance of the ground not allowing sufficient current to pass to 
heat the filament, but this kind of ground will be detected, 
nevertheless, by reason of the fact that the end of the wire 
will show a spark when the contact is broken. For this 
reason it is always better, when possible, to test in a mod- 
erately dark room. With this arrangement the operator can 
test his aparatus every day without trouble or inconvenience. 



However, you must bear in mind that when using an Edison 
three-wire system you cannot test any apparatus connected 
only to the neutral wire with a test lamp, because they are 
permanently grounded with the neutral. In testing with a 
dry battery it is not necessary to use a bell; just connect two 
wires to the battery, and make your test. If there Is a 
ground there will be a spark. It is better, however, to use 
two or more batteries connected in series. 

With the insulated three-wire system the test lamp acts 
the same as with the two-wire system. 


Figure 109. 

Locating a grounded coil in the rheostat is a deep, dense 
mystery to many operators, but it really is a very simple 
matter. Fig. 109 is a diagrammatic representation of a rheo- 
stat; A, B, C, D, etc., indicating the coils or grids, coil or 
grid E being grounded to the frame at X. Assuming that we 
wish to test this rheostat to find out whether or not it is 
in good order, using a magneto or bell and battery, first 
touch the binding posts with the two leads from the bell 
and battery, or magneto. If you get a ring it indicates that 
the circuit is complete; that is to say, no cojl js broken or 


disconnected. Next touch one binding post and the outer 
casing or frame of the rheostat. If you get no ring then 
the rheostat may be considered in good order, except for 
one thing which cannot be located with a bell or test lamp, 
viz., two coils being sagged together so as to eliminate a 
part of the resistance without breaking the circuit. 

The rheostat may be tested with a test lamp in a number 
of different ways. First, assuming the rheostat to rest upon 
a marble slab, or other insulating material, with the current 
on, touch your test lamp to the frame of the rheostat and 
to the wire of opposite polarity. If you get a spark, or light, 
the coils or grids are grounded to the frame, and the ground 
can be located as hereinafter described. Another way would 
be to disconnect the wire leading from the rheostat to the 
lamp from the rheostat binding post and, with the switch 
closed, touch the frame of the rheostat with one test lamp 
lead and the wire which has just been disconnected with 
the other, the arc lamp carbons being "frozen," i.e., in con- 
tact with each other. If you get a light or a spark there 
is a ground; if not, there is none. Still another way, again 
assuming the rheostat to rest on an insulating shelf, discon- 
nect one of the wires from the rheostat binding post and, 
with the carbons of the lamp frozen and the switch closed, 
touch the disconnected wire end to the frame of the rheo- 
stat. If you get a spark there is a ground. 

Now suppose you have applied one of these tests and 
find there is a ground in the rheostat, indicating that one 
of the coils is electrically connected with the frame. How 
are you going to locate the particular coil or grid at fault? 
This is a point which puzzles so many operators, yet it is 
as simple as a, b, c, when you come to examine it in the 
light of common sense. Close the switch, and, if you are 
using a test lamp, attach one test lamp lead to one of the 
rheostat binding posts. Now attach the other test lamp lead 
to the frame of the rheostat, and, beginning at the end far- 
thest from the binding post the test lamp lead is attached 
to, disconnect the first coil, which we will assume to be coil 
A, Fig. 109. The light still burns. Disconnect coils B, C, 
and D in turn. The light still burns. Disconnect coil E 
and the light goes out, because you have removed the ground. 
You will, therefore, proceed to examine coil or grid E and 
locate the trouble, which may and probably will be due to 
a ground through the insulation of the connection at Z. 

Where a rheostat consists of two blanks of coils or grids 
considerable labor can be saved by disconnecting one side 


or bank from the other, and then testing each, as a whole, 
to find out which half the ground is on. It is then only 
necessary to disconnect the individual coils on the defective 

It is always advisable that the projection machine lamp- 
house and mechanism be grounded to the metal of the opera- 
ting room, and the whole may, or may not be thoroughly 
and permanently grounded to a water pipe. The reason for 
grounding the projection machine, especially if it be an all 
metal one, to the operating room metal work, lies in the fact 
that if the machine be insulated from the metal of the 
operating room and the lamp should become grounded to the 
metal of the lamphouse it would charge the whole mechan- 
ism, and, should the operator, when putting a reel in the 
magazine, touch both the magazine and the metal of the 
operating room with the reel, there would be a spark which 
might set the film on fire. 

There is no real necessity for grounding the metal of the 
operating room; it may or may not be done, as best suits 
the ideas of the individual. 

Testing for ground is, after all, a matter of plain, horse 
sense, and anyone can do it if he understand electrical action. 


The Lamp House. Of late projection machine manufac- 
turers have awakened to the importance of a carefully con- 
structed lamphouse, and the later models of all standard 
projectors leave very little to be desired so far as the lamp- 
house be concerned. In the early days, when it was the 
exception to use in excess of 25 amperes for projection, and 
30 was about the limit, no one paid much attention to the 
lamphouse. It was a little, contracted affair, built of russia 
iron, single thickness, which merely served to confine the 
light, or some of it, and hold the condensers after a fashion. 

The lamphouse of the modern projector is, however, in 
some instances, a double walled affair, lined on the inside 
with insulating material. Its proportions are imposing; its 
ventilation is very carefully planned, and in fact the whole 
outfit is excellent and complete, and probably will not be 
very largely improved in the future, except as to the con- 
denser mount, which still leaves considerable to be desired. 

The ventilation of the lamphouse is of extreme importance, 
particularly where high amperage is used. If your lamp- 
house is of the type having screens over the ventholes, either 
above or below, it is very important indeed that these screens 


be kept perfectly clean, since if the screen, either above 
or below, clogs up, then ventilation is impeded and an ex- 
cessive heat is set up inside the lamphouse. This has a 
double effect. First, it tends to overheat the condensers to 
raise them to an unnecessarily high temperature, which very 
largely increases liability to condenser breakage through 
sudden and extreme contraction of the lens, especially when 
the lamphouse door is opened to trim the lamp immediately 
after finishing a reel. 

The lower the temperature in the lamphouse is kept the less 
zvill be the likelihood of condenser breakage. 

That is a plain, common sense proposition everyone ought 
readily to understand. It also is very plain that the more 
open and free the ventilation of the lamphouse is the lower 
will be the temperature of its interior. 

The second effect of lack of ventilation is that by increasing 
the temperature inside the lamphouse the lamphouse itself 
radiates more heat, thus increasing the discomfort of the 
operator in warm weather. 

The core of the carbons contains a substance known as 
water-glass, and the residue of water-glass is a white ash 
which coats the interior lamphouse walls and very quickly 
clogs the holes in the screen at its top. Therefore it be- 
hooves the operator to clean the top screen every day. It is 
not a dirty job if it is done every day, but if you try to clean 
it when it has not been cleaned in a long while you had 
better take the entire lamphouse off and take it out of doors 
to clean it or you certainly will have a nasty mess in the 
operating room. 

Best Method of Ventilation. The best and most feasible 
scheme for ventilation is one recommended by the Projec- 
tion Department of the Moving Picture World more than 
three years ago. It consists of running a 3 or 4 inch metal 
pipe from the top of the lamphouse to the open air, or up 
into the operating room vent flue. This is now provided for 
in the Power, Edison, Simplex and Baird lamphouses of late 
design by an opening left for that purpose. 

The idea is set forth in Fig. 110. This pipe carries away 
much of the heat of the arc, reduces the liability to condenser 
breakage and renders the position of the operator far more 
pleasant through the hot summer months. It has the hearty 
indorsement and approval of the Projection Department of 
the Moving Picture World and of the author of this book. 



/ would recommend its installation in all operating rooms, but 
don't just run a short piece of pipe up a foot or so above the 
lamphouse. It would be perfectly safe to do that, but it 
would not carry the heat outside the room, and, more- 
over, would not be approved by the authorities in cities. 
Run the pipe out to the open air or up into the operating room 
vent flue. If this is done it need not be capped with a screen, 
because in any event it will not be less than 5 or 6 feet long, 
and by no stretch of the wildest imagination would a spark 
from the electric arc reach such a distance as that. If it is 
necessary to swing the lamphouse over to the stereopticon, 

Figure 110. 

that can be readily provided for by putting in a swing joint 
or a slip joint, or a combined swing and slip joint. Most of 
the leading machine manufacturers have already made pro- 
vision so that this sort of vent pipe can be attached to their 
lamphouse. Where suc'h provision is not made the pipe may 
be attached by cutting through the top of the lamphouse and 
attaching it thereto with a suitable flange. 

In most cities the authorities require that the back of the 
lamphouse be entirely inclosed. This is pure, unadulterated 
nonsense, but nevertheless when it is the law it must be 
complied with. Where the law does not require its closure, 


however, I recommend that the entire back of the lamphouse 
be left open, unless such a pipe as already described is in- 
stalled, in which case there will be ample ventilation without 
removing the back. 

Lack of ample ventilation in the lamphouse causes moving 
picture theatre managers in this country a large sum in con- 
denser breakage every day. I should say this item alone would 
run to at least two and perhaps as much as five hundred dollars 
a day, in the United States alone, meaning that that amount of 
condensing lenses are broken that would not be broken if the 
lamphouse had ample ventilation. 

Keep Your Lamphouse Clean. The careful, painstaking, 
competent operator will keep his lamphouse clean. It does 
not look well to find a half inch of carbon dust, dirt and 
pieces of broken carbons lying on the floor of the lamp- 
house. It does not give one a good impression of the man 
in charge. It is not the workmanlike way of doing things. 

The rods upon which the lamphouse slides, if it slides over 
to the stereopticon, should be kept lubricated. When your 
lamp has the desired angle, if the lower carbon jaw comes 
into contact with the front wall of the lamphouse you should 
line the front wall at that point with one-eighth inch as- 
bestos millboard, which may be fastened to the wall by 
punching four screw holes and attaching the board with 
small, short stove bolts. If your lamphouse is of the old, 
unlined type it is also an excellent plan to rivet one-eighth 
inch asbestos millboard to the left hand wall, or door, op- 
posite the binding posts of the lamp. Many annoying grounds 
are caused by a stray strand of the asbestos-covered lamp 
leads protruding and making electrical contact with the lamp- 

Arc Projector. Modern lamphouses are provided with a 
properly located arc observation window of ample dimen- 
sions, fitted with glass of a color combination enabling the 
operator to look directly at the arc without the least eye- 

Many operators, however, prefer to project a picture of 
the arc on a white screen pinned to the operating room wall. 
This is very easily done, as follows: With a drill or punch 
not exceeding one-thirty-second of an inch in diameter, make 
a hole in the left hand wall, or door of the lamphouse exactly 
opposite the arc when it is in proper position. Through this 
hole a picture of the arc will be projected to any white sur- 
face held a short distance away, but the image will be upside 



down. The picture may be improved by placing in front of 
the hole a small piece of a broken condensing lens, or any 
small lens you may happen to have; an old spectacle lens 
will often serve. It is also possible to project a front view 
of the arc on the front of the upper magazine of the pro- 
jector by punching a small hole in the front wall of the 


Figure 111. 

lamphouse just above 
the condenser casing. 
Don't have the hole 
too large, however, 
or the image will 
not be sharp. 

Condenser Holder. 

It is only of late that 
any particular atten- 
tion has been paid to 
the condenser holder, 
but several holders 
have now been 
evolved, the intelli- 
gent use of which 

very largely eliminates condenser breakage. 

Condensers break because one part of the lens is thin and 
another part is quite thick. Therefore when the lens is sub- 
jected to heat, the edge, or thin part, heats up very rapidly 
as compared to the thicker center. Hence the edge of the 
lens expands and contracts much more rapidly than its 



The theory of these improved condenser holders is that by 
providing a heavy band of metal at the edge of the lens 
there will be a retarding effect in the metal which will hold 
down the temperature of the edge of the lens when it is 
heating up, and hold up its temperature when it is cooling 
off, so that the center and edge of the lens will cool down 
approximately at the same speed, and thus expansion and 
contraction will be fairly equal and breakage very nearly 
eliminated. The theory is correct, as has been proven in hun- 
dreds of instances where these holders have been installed. 

In Fig. Ill we see four styles of the Elbert holder illus- 
trated. I think the 
idea is fairly well con- 
veyed by the pictures. 
The lens is held in 
place by spring steel 
ring, marked X in the 
illustration. The El- 
bert holder may be 
used for both the front 
and back lens, and in 
fact as made for the 
Simplex and Motio- 
graph it does ,hold both 
the front and back 
lenses. The Power and 
Edison 'holder is made 
for one lens only, but a 
pair may be secured, if FREDDY HOLDER 

desired, so as to hold Figure 112. 

both lenses. 

In Fig. 112 is shown the Preddy holder, also an excellent 
and very efficient device for holding the rear lens of the con- 
denser. It is not, however, designed to hold the front lens. 
Fig. 113 shows the method of its installation and the details 
of its construction. It is made of cast metal. 

No doubt machine manufacturers will themselves add this 
feature to their projectors in the near future. In fact some 
of them have already done so, in a limited way. / would 
strongly advise all theatre managers to have their lamphouscs 
equipped with one of these devices, particularly if they are using 
high amperage. To those troubled with condenser breakage 
these holders zvill save their cost in a very short time. Both' 
the Preddy and Elbert mounts are excellent and easy to install. 



In ordering give the kind and model of your projector. Don't 

forget that part, for it is very necessary. 
The Lamp. Light is the very foundation of projection, and 

the lamp is a most important factor in the production of good 

light. In fact, the production of the best possible projection 
light is entirely out of the question 
where a poor lamp is employed, or a 
lamp that is dry, loose and "wobbly," 
or so tight in its joints, or so dry, 
that you can scarcely move its 
adjustment wheels. 

In the past two years there has 
been an enormous improvement in 
the design of projector lamps; in 
fact it is only within that time that 
we have had anything like an efficient 
lamp. The manager who is compel- 
ling his operator to use an old anti- 
quated type of lamp is doing a very, 
very foolish thing. He is "saving at 
the spigot and losing at the bung- 

Figure 113. 
hole." He is injuring the results on his screen every hour he 

runs, merely to save a few dollars in the purchase price of a 
good lamp. 

Many an operator is producing poor results on the screen 
for no other reason than (a) he has an old out-of-date lamp, 
not having the proper adjustments; (b) his lamp is not 
properly lubricated; (c) it has too much lost motion and 
shakiness; (d) his lamp is too tight or too dry to allow of 
his making proper adjustments of the arc; (e) its carbon 
jaws are rough and dirty, thus preventing good contact be- 
tween the carbon and metal. 

It matters not how excellent the lamp itself may be, unless it 
be kept in proper condition and properly lubricated it cannot be 
handled properly and, therefore, the operator cannot make the 
fine adjustments of his arc which are absolutely necessary to 
good projection. 

The lamp should be taken apart at stated intervals and thor- 
oughly lubricated with powdered graphite. It is of little use to 
lubricate the lamp with grease or oil, since it is quickly burned 
off or dried by the heat, besides making a smudge inside the 
lamphouse which is likely to cloud the lenses. 

Managers should in all cases provide plenty of good, powdered 
graphite t and compel, if necessary, their operators to use it regu- 
larly on the lamps. 


Seventy-five cents will get a can large enough to last for 
a year of more, unless it be wasted. By all means get a can 
at once unless you already 'have it. Powdered graphite may 
be had of up-to-date dealers. If you fail to get it elsewhere 
it may be had of the Picture Theatre Equipment Company, 
19 West Twenty-third street, New York 20 cents, by parcel 
post. This company has it both dry and in a paste form 
both good. Say which you want when ordering. 

Operators should make it a practice to take their lamp 
entirely apart, except the insulated joints, which should never 
be disturbed, once a week if they are running a twelve-hour 
show and using heavy amperage, or say once in two weeks 
if the running time does not average more than five hours a 
day. Take out all the screws, dip them all in oil, wipe them 
off clean and dip them in a box of graphite; also smear all 
the moving parts with oil, wipe the oil off and rub the parts in 
graphite; the oil is merely to make the graphite stick. There- 
fore all surplus oil should be wiped off clean. Don't wipe the 
parts off after dipping them in graphite. Just shake the 
graphite off and put the parts back. The more graphite 
adhering to them the better. If you have never done this 
you will be astonished at what a difference it will make in 
the handling of your lamp and your arc. You will be sur- 
prised at how much better you can gauge your light. 

Make it your practice to take out the carbon clamp screws 
every day before starting the run, and lubricate them with 
graphite as before set forth. 

Do this and you won't need to twist them up with a plier; 
in fact, if you have been using unlubricated clamp screws you 
will most likely crush the first carbon or two you put in. 

On Pages 270, 271, and 272 will be found illustrations of the 
lamps of the various leading projection machines. These 
are given in order that the operator may examine the gen- 
eral make-up and decide for himself which is best. To this 
end certain letters have been incorporated. 

(a) Being the carbon feed handle; (b) the handle with 
which the lamp, as a whole, is raised up or down; (c) the 
handle by means of which the lamp is pulled back or shoved 
ahead; (d) the handle by means of which the whole lamp 
is swung from side to side; (e) the handle by means of which 
the upper or lower carbon is swung to one side in order to 
accomplish the side-lining of the carbons: (f) the handle 
by means of which the upper or lower carbon is shoved 
ahead or pulled back in order to govern the formation of 
the crater; (g) the carbon clamp screws; (<h) the insulation; 




(i) the means by which the carbon arms may be tilted or 
angled; (j) the hooks to hold the cables; (k) the means by 

which the whole lamp 
is angled. 

It will be noted that 
these lamps are far 
more substantial than 
the older types. They 
accommodate 12-inch 
carbons above and 6- 
^^^ inch below. They are, 

t" * ' JHSfik without exception, well 

k . made mechanically, and 
..,;4|JHV have all the necessary 

adjustments to enable 
the operator to force 
his arc into any desired 
position. The old 
nuisance of weak car- 
bon clamps has been 
done away with. It is 
rare indeed to hear of 
an operator breaking a 
carbon clamp on the 
newer type of lamp. 
The small rack bars 
have given place to 
bars of generous di- 
mensions, and, in fact, 
the modern lamp leaves 
very little to be desired. 
It is extremely im- 
portant that the inside 
of the carbon clamps 
of your lamp be thor- 
oughly scraped out once 
a week; oftener if high 
amperage is used. 

Through continued 
use the inside of the 
carbon clamp gradually 
becomes rough, pitted 


Figure 114A. 

and dirty. If left un- 

cleaned it is but a question of time when it will be practically 
impossible to secure good contact between the carbon and the 



metal. The proximity of the arc operates to create high 
temperature in both the metal and carbon and when you add 
to this the heating effect of poor contact the result is very 
bad indeed. Needling of 
the carbons also may be 
often traced to this 
cause. The result of 
this kind of treatment of 
the carbon arm, if long 
continued, is permanent- 
ly to raise its resistance. 
The moral is, keep your 
carbon contacts perfectly 
clean, not sometimes, but 
always. No. y* emery 
cloth wrapped around a 
small file makes an ex- 
cellent cleaning tool. 

Asbestos Wire Lamp 
Leads. The asbestos 
wire lamp leads should 
be attached to the car- 
bon arm by means of 
a wire terminal similar 
to those shown in Fig. 
29, Page 87. See Page 
50 and Page 233 for 
further important mat- 
ter on the subject of 
lamp leads. 

Be sure that your 
lamp wire contacts are 
kept perfectly clean. 
They should be well 
polished at least once 
every week. Metal 
oxidizes under the ac- 
tion of heat, and the 
scale thus formed, 
while very thin, has 



Figure 114B. 

high resistance. Due to this fact it is difficult to maintain good 
electrical contact at these connections. The scale may be al- 
most invisible, but it is likely to be there just the same, 
particularly if a copper wire-terminal is used. 




Lamp Insulation. 
The insulation between 
the carbon arms and 
the body of the lamp 
must, of course, be per- 
fect. A ground is often 
formed through carbon 
dust settling on the 
lower carbon arm and 
forming a bridge across 
the insulation. This sort 
or ground would not 
carry much current, but 
it is likely to give the 
operator a good, lively 
shock just the same, if 
the lamphouse is insu- 
lated and he is grounded. 
If, on the other hand, 
the lamphouse is ground- 
ed there may be a con- 


Figure 114C 


stant though slight loss of current. The moral is, keep the 
dust brushed off the top of your lower carbon arm. 

The insulation of the lower carbon arm should project 
above the surface of the metal at least one-eighth of an inc'h. 
If it does not, loosen the joint and insert a piece of mica, 
allowing it to do so. 

Lamp Adjustments. The modern lamp has the following 
adjustments, all capable of being made by means of adjust- 
ment wheels outside the lamphouse. (a) The whole lamp up 
and down; (b) the whole lamp backward and forward; (c) the 
arc itself sidewise; (d) movement of rack bars to feed the 
arc; (e) side movement of upper or lower carbon independent 
of its mate; (f) movement backward or forward of the upper 
or lower carbon independent of its mate. These independent 
carbon movements, e and f, are of much importance, since 
only by their use can the crater properly be handled and 
compelled to form in the proper position. (See "Setting the 
Carbons," Page 290.) 

The backward and forward movement of the whole lamp 
should be accomplished by means of a very coarse screw or 
its equivalent, since it is foolish to be compelled to give the 
adjustment wheel half a dozen turns in order to move the 
lamp a quarter of an inch. 

Angle of the Lamp. The angle at which the lamp should 
be set is varied somewhat with the kind of current and 
amperage. For direct current it is sufficient to say that the 
angle should be as much as it is possible to give without 
causing the lower carbon tip to interfere in the light. (See 
"Carbon Setting," Page 290.) With A. C. the same thing is 
true, but one has to use considerable more care when deal- 
ing with A. C. unless the amperage be above 60, since the 
crater is very small. 


The motor driven machine is a fixture. I believe it fairly 
may be said that from SO to 75 per cent of the present output 
of the projector factories are equipped with motor drives, 
and at least one manufacturer equips his entire product thus. 

The motor driven machine is an unquestioned blessing to 
the operator, though unfortunately it is a blessing which 
may very easily be and all too frequently is abused. The 
author has long since taken the position that there is only 
one proper place for the operator while the picture is being 
projected, and that is right . beside his machine, with his 


eyes on the screen every instant of the time. With the hand 
driven machine he is compelled to stay there, and that is the 
chief advantage urged for the hand drive. However, the 
driving of the projector by hand involves a very distinct 
hardship for the operator, particularly where there is only one 
employed. It means that for from three to eight hours, or 
even longer, he is compelled to turn a crank continuously, 
and this task is made none the easier by the knowledge that 
with a comparatively nominal first cost outlay and slight 
expense thereafter all this drudgery could be performed by 
a motor. 

By the adoption of an ordinance requiring that the motor 
circuit be controlled by a switch held normally open by a 
spring (the Massachusetts law) and making the penalty for 
holding the switch closed by anything except the operator's 
hand punishable by revocation of the theatre license for two 
days for first offense and ten days for each subsequent 
offense, the operator may be effectively located at the pro- 
jection machine, where he belongs. 

There is another objection to the motor, that is, as a gen- 
eral proposition the speed of a motor driven projector can 
not or at least will not be regulated to suit the action in the 
picture as closely as it can and probably will be where a 
projector is hand driven. This, however, is not or at least 
would not be a serious objection if some scheme be devised 
to keep the operator at the machine, where he belongs, 
because with the more up to date motor driven projectors it 
is possible to change the speed quickly, and with a fair 
degree of accuracy. 

There are a number of types of motor drives. Almost every 
machine has a speed regulating device of its own, and of 
course each manufacturer claims his to be the best. They 
are all excellent devices of their kind, and of course the 
particular one put out by each machine manufacturer is 
especially designed and adapted for use on the machine 
made by that manufacturer, and will probably give better 
satisfaction on those machines than will any other. The 
mechanical construction of these various drives are shown 
under the head of "Mechanisms." 

In addition to this, however, there are a number of motor 
drives made by individual manufacturers for use on old 
style projectors or on the newer projectors which are not 
equipped with a regular motor drive. Two of these which 
are excellent, and can be recommended by the author, are 
the John D. Elbert Friction Speed Controller and the Freddy 



Speed Controller, both of which are moderate in price and 
give very satisfactory service. 

Elbert Speed Controller. Fig. 115 is an illustration of the 
Elbert Speed Controller. The action of this device is very 
simple, and it readily may be applied to any make of ma- 
chine; also it may be operated in conjunction with any style 
of either A. C. or D. C. motor. In Fig. 115, M is a cast iron 
disc 4 l /2 inch diameter, rigidly attached to the same shaft 
carrying two-speed pulley A; G is an iron disc, or plate, 
between which and a smaller one on the opposite side is 
clamped friction material H, which impinges upon iron disc 
M. Wheel G is rigidly attached to shaft E, which, together 
with shaft K, forms a carriage which slides endwise through 
standards J and L, the 
end motion being con- 
trolled by regulating 
wheel C, which op- 
erates screw F, thus 
moving rods E and K, 
wheel G and pulley B 
endwise. The action 
of this is to alter the 
distance of wheel G 
from the center of 
wheel M, and no mat- 
ter whether the motor 
be attached to pulley 
B and the projection 

Figure 115. 

machine to pulley A, or vice versa, any alteration of the 
distance of wheel G from the center of disc M will, of 
course, alter the speed of the projector. It will thus be 
seen that this adjustment in conjunction with two-speed 
pulley A will make possible the graduation of the speed 
of the projector to any desired value. The amount of 
friction between wheel G and disc M is controlled by 
spring D, and the end thrust thus set up is carried by ball 
bearing N. The amount of friction provided by spring N 
is adjustable, and should be only sufficient to prevent slip- 
page between wheel G and disc N, since any excess would 
cause the motor to consume unnecessary power; also it 
would cause unnecessary wear on the parts. This device is 
compact, and is provided with nickled compression grease 
cups. Its price is $15, and may be shipped parcel post. 
Pulley B, to which the machine is presumed to be belted, 



does not move endwise with shaft E, but by a very simple ar- 
rangement remains stationary, although rigidly attached to 
the shaft so far as the driving power be concerned. The 
position of pulley B and governing wheel C and screw F 
are interchangeable, that is to say, these parts may be made 
to change places, so that governing wheel C can be at either 
side of the device, as is most convenient to the operator. 
On many machines the device may be conveniently placed on 
a baseboard, or stand, between the lamphouse and mechan- 
ism, with the motor underneath, but the position will vary 
with local conditions. 

Freddy Speed Controller. Another excellent device is the 
Freddy Speed Controller, illustrated in Fig. 116, in which 
the parts of the controller are shown very plainly. It may 

be used with any make 
of projector or with 
any kind of A. C. or 
D. C. motor. Six is a 
disc wheel, carrying 
cone pulley 3, to which 
the projector is belted. 
Friction Wheel 1 car- 
ries a cone pulley to 
which the motor is 
belted. Friction wheel 
1 is attached rigidly to 
shaft 7, wLich is moved 
endwise by handle 6. 
This endwise move- 
ment alters the point 
of contact between 
friction wheel 1 and 
disc wheel 6 with rela- 
tion to the center of the latter, and as will be readily seen any 
change in this respect will instantly alter the speed of disc 
wheel 6 and cone pulley 3, to which the projector is belted. 
This feature, taken in conjunction with cone pulley 3 and 
the cone pulley carried by friction wheel 1, provides a very 
wide and finely graduated range of speed for the projector. 
The amount of friction between wheel 1 and disc 6 is de- 
termined by coil spring 5, and the compression of this spring 
may be readily altered by moving the set collar at its end. 
The end thrust thus set up is carried by ball bearing 4. 
In Fig. 117 the method of attachment is illustrated. It is 

Figure 116. 



important that the motor be placed not less than 18 inches from 
a cone pulley 1, Fig. 116. The bottom lever 6 is carried by a 
small bolt or screw. If the lever shows a tendency to work 
either way of its own account tighten this bolt or screw. 
This controller costs $12.50. It may be shipped parcel post. 

Multiple Clutch Controller. J. Claude Re Ville, Florence, 
S. C., also makes a multiple clutch controller, illustrated in 
two forms in Fig. 118. This is a line shaft scheme by means 
of which one motor drives two machines. The drawings, I 
think, explain themselves. Either style of these clutches is 
claimed to be an improvement over using two motors, be- 
cause of the perfect control obtained over either machine while 
seated at the other. These clutches are made and sold, so 
Brother Re Ville says, at about one-third the price of a 
good motor, and they are guaranteed by their makers to 
give satisfaction. 

I do not myself think 
very much of the up- 
per one, because it 
seems to me that either 
the belt would have to 
slip or the machine 
start with a jerk. The 
lower cone clutch, 
however, ought to 
work perfectly. 

A fairly good speed 
controller may be con- 
structed as per the idea 
illustrated in Fig. 119. 
This device can be 
made efficient, but the 

cones must not have too steep a pitch, and the shafts must 
be in good alignment or the belt won't run right. In fact 
this cone idea is perhaps the simplest and best of any 
home-made speed controller I have examined. It is cheap, 
efficient, and fairly durable. I would, however, as a general 
proposition, advise operators and managers to purchase the 
regular motor drive attachment put out by the manufac- 
turers of their machines. 

In designing a home-made drive it should be remembered 
that crank speed should have a variation of about 45 to 70. 
/ would caution operators against belting a motor to the fly 
wheel of their projector. The fly wheel of a projector is 

Figure 117. 



mounted on the shaft carrying the cam. It is a high speed 
shaft, and in any event its bearings wear pretty fast. If in 
addition you add the strain of a belt the wear is increased, 
and wear in the cam shaft bearings has an immediate and 
bad effect on the intermittent movement, and, therefore, on 
the picture on the screen. My advice is to never under any 
circumstances belt your motor drive to the fly wheel of your 
projector. I would also advise operators and managers who 
build a home-made motor drive to limit the possible crank 
shaft speed to 70. Seventy is as fast as any projection ma- 
chine ought to be run under any ordinary conditions; the 

Figure 118. 

limit the other way should be 45; below that the fire shutter 
is apt to drop. 

Where motor driven machines are in use, the temptation to 
the operator to leave his machine, at least for short intervals 
of time, is strong. The manager is also inclined to have the 
operator utilize in rewinding, making splices, etc., what ap- 




pears to him to be wasted time while the picture is run- 
ning. Many otherwise good operators do this, too, but I 
cannot condemn the practice too strongly. I have said 
literally hundreds of times, and I say again, as emphatically 


THE PROJECTION, governing the speed, and regulating his light. 
The temptation to leave the machine is still greater if in addi- 
tion to a motor drive an arc controller is used, and, in some high 
class houses, where high class projection is -put on, I have 
gone into the operating room and found the operator away 
from his machine, and have had him stand and talk to me 
for as long as two 
or three minutes 
while the motor and 
the arc controller 
ran the show. The 
fact that there was 
no fault in the 
screen illumination 
during that time 
does not alter the 
fact that there might 
have been, and if 
there had been the 
operator would not 
have known it, and 
certainly he was in no position to properly regulate the speed of 
his projector under the varying conditions met with in different 
scenes of the film. I must again impress upon operators 
the fact that if they themselves, by their actions, convey the 
idea to the manager that it is not necessary to watch the 
picture, govern the machine speed, and be on the job every 
minute of the time the picture is running, the manager is 
very likely to become imbued with the idea that, equipped 
with a motor drive and an arc controller, there is no large 
need for high grade skill in the operator himself. This view 
is wrong, from any and every point of view, but nevertheless 
if managers get that idea operators have none but themselves 
to blame. I would also like to impress upon the minds of 
operators the fact that when the manager gets the aforesaid 
idea fixed in his mind it is prettly hard to convince him that 
there is any need of paying operators good salaries. The 
moral of this is: stay at your machine, watch the picture, 

Figure 119. 


graduate your speed to fit the movement in the film, and 
let tl*e manager understand that, while automatic arc con- 
trollers and motor driven machines improve conditions and 
results, still by no manner of means do these lessen the 
necessity for knowledge and skill on the part of, the operator 


The Walstad Machine Company, Tacoma, Washington, 
constructs a very substantial, rigid stand, designed to allow 
the driving of two or more projection mechanisms of any 
standard make with one motor, the motor driving a counter- 
shaft which is equipped with separate clutches for each of 
the projection mechanisms, as well as a friction for driving 
the rewind, which is also located on the stand between the 
projection machines. There is also a large substantial fric- 
tion, by means of which the speed of the projection mech- 
anisms may be varied at will. One advantage of this ar- 
rangement is that the speed of both projection mechanisms 
is precisely the same when dissolving from one picture to 
the next. 

All machine controls are located in such manner that the 
operator is enabled to handle the equipment with ease, 
efficiency, dependability and safety. The operator handles 
both machines and the rewind while standing or seated be- 
tween the projectors a very favorable feature where one 
operator is compelled to do the rewinding in addition to 
handling both projectors. I object strenuously to the 
operator doing the rewinding, but that is nevertheless the 
practice in many theatres. 

In order to accomplish this the magazines of the right- 
hand machine are reversed (full directions for accomplishing 
this accompany the outfit), so that the operator threads the 
right-hand machine from the left-hand side. This is rather 
awkward at first, but he soon gets the knack of it, and he 
can then thread just as readily from one side as the other. 

Another feature is a brake on the unwinding reel of the 
rewind. This brake is automatic in its action, and by its use 
the film is wound tightly upon the reel, which eliminates 
the necessity of using the hand as a brake and "pulling 
down," which latter operation is responsible for much of the 
damage to film. 

The main driving shaft is mounted upon a separate frame, 
to which is also attached the motor, thus making the power 
section a complete unit within itself. This unit is attached 



to the main stand by means of two brackets, as can be seen 
in figures 120 and 121. 

The stand is substantially constructed of iron and steel 
throughout. It is rigid and. so braced that vibration is re- 
duced to a minimum. There is also provision for all neces- 
sary adjustments, so that the operator can readily set the 
apparatus to give any desired pitch in projection. The motor 
belt is very heavy and substantial. This stand has been in 

Figure 120. 

use on the Pacific Coast for some years, and is no longer 
an experiment. Where the Walstad stand is installed, the 
theatre will, of course, only purchase the projection mech- 
anisms, lamphouses and magazines. 

Fig. 121 gives a very good idea of the quipment as a 
whole. The bases upon which are mounted the projection 


mechanisms are shown at 1-1. They are made to fit any 
standard projection machine. Provision has been made to 
attach the lower .magazine to the underside of the bases. In 
the case of the right-hand machine the upper and lower 
magazines are reversed, so that the doors open toward the 
center of the projection stand, as has already been noted; 
2-2 are the bases upon which are mounted the lamphouses. 
These are also made to fit the various standard lamphouses; 
3 is the motor which drives the complete equipment, and may 
be had for either A. C. or D. C. The base to which the 
motor is attached is so made that it will accommodate any 
standard motor of suitable size; 4-4 are the clutches by 
means of which the projection mechanisms are driven; 5 is 
the rewind drive; 6 is a glass inserted in the steel plate, with 

Figure 121. 

a low C. P. incandescent lamp underneath for making patches 
and for inspection; 7-7 are the handles which control the 
clutches; 8-8 show the method of adjustment for pitch by 
means of screws, there being a similar arrangement on the 
rear legs. In Fig. 120 they are shown more clearly; 9-9 are 
lamp sockets, designed to hold incandescent lamps which 
swing in front of the lens during threading, for the purpose 
of framing; they may also be used for locating proper posi- 
tion of carbons after trimming the lamp. 

To Operate Stand. Place framing light in front of the 
objective of the left-hand mechanism. Thread film in usual 
way. Remove left-hand framing light. The motor having 



been started, all that is necessary to start the left-hand 
machine is to drop the opening lever into operating position. 
If the speed of the machine is not satisfactory, move the 
control lever toward the motor to decrease speed, or away 
from the motor to increase it. Having got left-hand head 
under way at the proper speed, proceed to thread the right- 
hand head the same as you did the other. When the time 
comes to change over, all that is necessary is to drop the 
operating lever of the right-hand machine into operating 
position, after first striking your arc, of course, and when 
the dissolve is completed pull the lever of the left-hand 
machine into non-operating position. 

In changing from one reel to the other no attention need 
be paid to the speed of the machine, unless it is desirable 
because of the action in the picture, since both machines 
will, of necessity, be running at precisely the same rate of 
speed. If it is desired to run the show to schedule this may 
be done by observing the location of the lever, according to 
the marks on its segment. 

The author has personally examined this equipment a. id 
pronounces it first-class in every respect. 

Opportunities have no 
schedule time! You 
must be at the station 
when they arrive. 



THE very foundation of the projection of pictures, either 
moving or otherwise, is light, and light for projection 
purposes depends, to a very great extent, upon the 
electrodes (carbons) with which it is produced. 

Each form of arc lighting requires the use of carbons 
differing in material, physical characteristics and methods of 
manufacture. For projection work it would be utterly im- 
practicable to- use either very, hard carbons or the com- 
paratively soft, solid, impregnated flame carbons. If one 
attempted to use these carbons the result on the screen 
would be far from satisfactory. 

The National Carbon Company has very kindly consented 
to describe for us in detail the process of carbon manufac- 
ture as follows. 

Manufacture. The manufacture of projection carbons re- 
quires more care than any other type of lighting carbons, 
on account of the necessity for high candle power, steadiness, 
reliability, color and other features. The basis of the pro- 
jection carbons is lampblack, the purest form of carbon 
known. Even the ordinary lampblack used in the manufac- 
ture of other types of lighting carbons contains far too 
much ash to be used. Therefore a special, selected black is 
employed. Even this material contains considerable volatile 
matter, which is driven off by calcination at a high tempera- 
ture. This calcined material is known as "carbon flour," 
and is so pure that it is less than one-twentieth of 1 per 
cent, ash, and contains little or no volatile matter. To this 
flour is then added a high grade binder and it is machine- 
mixed into a stiff mass, in a fashion very similar; to that 
employed in kneading bread dough, after which it is made 
up into plugs and fed into the cylinders of hydraulic presses, 
which force it through suitable dies. As it comes from the 
presses the carbon is allowed to run on grooved boards, 
made for the purpose. It is now in the form of rods, approx- 
imately four feet long. Carbons which are to be cored are 
forced with a central hole throughout their length, made by 
having- a steel pin fixed in the center of the hole in the die. 
The carbons are now ready for baking. 


The form of the binder contained in the green carbon must be 
changed by driving off the volatile matter therein and depositing 
the rest throughout the electrode in the form of pure carbon. 
Inasmuch as the quality of the finished carbon depends on 
the method and temperature of the baking, this is one of 
the most important operations in its manufacture. The green 
carbons are first packed in special cylinders, to keep them 
from becoming crooked, and to protect them from injury, 
and are then placed in ga&fired furnaces specially designed 
to secure uniform heating', from which, during the process 
of baking, air is excluded. The total operation of packing, 
baking, cooling and unpacking takes from three weeks to a 

After removal from the furnace the carbons are cut to 
proper length and sorted for straightness. Owing to varia- 
tion in shrinkage during the baking process, some deviation 
from perfect straightness must be expected. The solid and 
hollow carbons are now separated. The former are taken 
directly to the pointing machine, after which they are ready 
for shipment; the latter go to the coring department. Here 
the central hole through the carbon is filled with the core 
material, which is a non-flaming but arc-supporting sub- 
stance. It is mixed into a thin paste with water glass, a 
soluble alkaline silicate, which becomes solid when dried. 
This core material is forced into the hole, and the carbons 
are then rebaked for a short time at a comparatively low 
temperature, in order to solidify the cores, and this opera- 
tion completes the process of manufacture. 

The purpose of the core is as follows: At its incandescent 
tip it supplies a far greater amount of arc-supporting gas 
than does the carbon composing the shell, and, therefore 
a path of lower resistance is offered between core and core, 
as in the A. C. arc, or between core and solid carbon tip as 
in the D. C. arc, than between two solid carbons. Hence 
the arc tends to emanate from the core, instead of wander- 
ing all over the face of the carbon. The practical effect of 
the core is to hold the light steady. If a solid upper carbon 
were used the light would jump from side to side and up 
and down, causing constantly recurring shadows upon the 
screen. It would be utterly impossible to secure a good, 
steady light with two solid carbons or with a solid tipper 

Size of Carbons. The size of carbons is a subject ap- 
proached with considerable hesitation. There is a growing 
tendency among operators to use three-quarter inch cored 


above and five-eighth inch cored or solid below, or anything 
between 40 and 50 amperes D. C. This practice is approved 
by some of the best operators in the country men in whose 
judgment I have confidence. They have tried five-eighth 
inch above and below, five-eighth inch above and one-half 
inch below, three-quarter inch cored above and below, three- 
quarter inch cored above and three-quarter inch solid below, 
and have finally decided that the three-quarter inch cored 
above and five-eighth inch cored or solid below is best. 
Therefore, I recommend those sizes to operators using be- 
tween 40 and 50 amperes D. C. There is considerable difference 
of opinion as to whether the lower carbon be solid or cored; 
therefore I would advise each operator to try both and decide 
for himself which gives best results in his case. Between 20 
and 40 amperes I would advise five-eighth inch cored above 
and one-half inch cored or solid below for D. C. Below 20 
amperes D. C. I think one-half inch cored above and three- 
eighth inch solid or cored below will serve the purpose 
very well. For A. C. on anything below 60 amperes I would 
recommend two five-eighth inch cored carbons above and 
below, and above 60 amperes, say up to 80, two three-quarter 
inch cored. Some operators using A. C. prefer a lower carbon 
of smaller diameter, so that it will needle considerably. This is 
a matter upon which I cannot pass, each one must experiment 
and decide for himself. 

Solid vs. Cored Lower. The objection to a solid lower 
carbon for D. C. is that it does not maintain as steady an arc 
as with two cored carbons. The objection to a cored lower car- 
bon is that, while it helps maintain a steady arc, this is only 
true by reason of the increased volume of gas emanating from 
the lower core, and this forms a curtain in front of the crater, 
and materially diminishes the illumination. 

I would not, under any circumstances, advise the use of 
less than 40 amperes A. C. for the projection of moving 
pictures. For stereopticon, however, the amperage may run 
as low as 25, or possibly even 20 if the picture be a small one 
and the screen of a semi-reflective type. 

As against the above the National Carbon Company pro- 
poses the following, with reference to carbon sizes and com- 
binations, and, inasmuch as it comes from a large carbon 
manufacturing company, it is certainly entitled to very seri- 
ous consideration on the part of operators. It will be 
observed that the recommendations made by the National 
are pretty closely in accord with those made by the author, 



and, inasmuch as each arrived at his conclusion entirely in- 
dependent of the other, I feel rather flattered to know that 
my recommendation coincides so nearly with v hat of the 

Amperage Upper 
70-80 %" cored 
60-70 %" cored 
50-60 %" cored 
45-50 9/16" cored 


Amperage Upper 


%" cored 


%" cored 

%" cored 

%" cored 


%" cored 

%" solid 

%" cored 


%" cored 

%" solid 

9/16" cored 

or cored 

%" cored 

9/16" solid 


%" cored 

%" solid 


9/16" cored 

7/16" solid 


%" cored 

r </16" solid 

Inspection. When purchasing carbons the operator or 
manager should inspect them for faults. Cracks running 
lengthwise of the carbons do no harm. They are in ,a way 
characteristic of the product, and are caused by the stiffness 
of the paste from which they are formed. Deep cracks 
running around the circumference, however, condemn the 
carbons, since there would be a tendency to break off at 
these points. Hair cracks running around the circumference, 
however, are often found in good carbons; they are due to 
the same cause as the longitudinal cracks and are of no con- 

Hard Spots. There is possibly no other one thing so 
trying to the operator as carbons containing hard spots. When 
the arc strikes a hard spot in the carbon the light will jump 
and sputter, in spite of everything that can be done, until the 
spot has burned away. These spots are belived to be caused 
by a lack of thorough mixing in the early stages of manu- 
facture. The manufacturers of the best carbons have prac- 
tically eliminated this most serious fault. 

Hard and Soft. Carbons that are too hard have a tendency 
to produce a yellow light through faulty cratering and slow 
burning, with resultant short arc. These things naturally 
result in an unsteady light of low intensity. On the other 
hand carbons that are too soft burn away quite rapidly, but 
usually give a good light while they last. 

Stubs. Modern projection lamps accommodate 6 inch 
lower and 10 or 12 inch upper carbons. This eliminates much 
waste, as against two 6 inch carbons, since there is just so 
much "stub end" to each carbon, whether the carbon be 6 


inches or 10 inches long. In other words, if you are using 
6 inch carbons and are able to burn them down until there 
is an average of 2 inch of stub left, you will be wasting one- 
third of each carbon; on the other hand, if it be a 12 inch 
carbon the two inches of necessary waste would only be one- 
sixth of the carbon; therefore, the doubling of the length 
of the carbon cuts the waste in half. 

There are, however, those who claim that the additional 
resistance of the long carbon is objectionable. The fact of 
the matter is, however, that the difference as between a 
6 inch and a 12 inch carbon is too small a matter to be 
seriously considered, particularly in view of the fact that the 
resistance of a carbon decreases as its temperature increases. At 
any rate the constant annoyance of being obliged to reset 
the carbon every reel, together with the relatively large 
waste in carbon stubs where short carbons are used, more 
than balances the extra resistance loss of the long carbon. 
Actual experiments made by the writer show that with 50 
amperes flowing through a closed circuit the insertion of 
10 inches of a five-eighth inch cored carbon only reduced 
the current flow one ampere. 

Chemicalizing the Carbon. Many operators have experi- 
mented on a small scale in "chemicalizing" carbons, and in 
the opinion of the author, when it is rightly done, salt soaking 
has beneficial effect. Concerning this, however, the National 
Carbon Company has the following to say: "There is an 
impression current in some quarters that if the carbons are 
soaked in common salt brine, the harshness so frequently 
found in the light emanating from the A. C. arc can be soft- 
ened and improved. This is a fallacy,! inasmuch as the 
salt will almost immediately volatize out as soon as the 
electrodes become heated by the high current passed through 
them, and none of this material ever actually gets into the 

Now, with all due respect to the manufacturer in question, 
I am unable to agree with this, because what I have seen I 
have seen, and I certainly have witnessed an improvement 
in the light for which I could find no other explanation ex- 
cept salt soaked carbons. Untreated carbons placed in the 
same lamp did not produce the same effect. It is, however, 
only fair to manufacturers of carbons to say they spend 
much time and money, or at least the American manufac- 
turers do, and I presume the foreign also, in experiment- 
ing with chemicals, in an effort to procure a product equal 


if not superior to their competitors' brands at the same or 
lower cost. They have carried on exhaustive experiments 
on every point which in their estimation can have any pos- 
sible influence on the operation of the arc. With their ex- 
tensive laboratories and research department they have vastly 
better facilities for carrying on these experiments than the 
operator could possibly have. Therefore I would suggest 
that when an operator discovers something he believes will 
be beneficial let him communicate with the Projection De- 
partment of the Moving Picture World, which will lay the 
matter before the manufacturers. 

Care of Carbons. Carbons should invariably be kept in a 
dry place where they will not absorb moisture, since mois- 
ture in the carbons will be detrimental to projection light. 


Since both lens and carbon diameter measurements are 
often quoted in millimeters it is advisable that the operator 
know what a millemeter means in fractions of an inch. 

One millimeter equals .03937 of an inch, or roughly one- 
twenty-sixth of an inch. The equivalents from 10 to 26 are 
as follows: 


Fractions of an Inch 
Millemeters in Decimals Roughly 

10 .3937 or 4/10 inch 

15 .59055 or 6/10 inch 

16 .62992 

17 .66929 

18 .70866 or 7/10 inch 

19 .74803 or 3/4 inch 

20 .78740 

21 .82677 or 8/10 inch 

22 .86614 

23 .90551 or 9/10 inch 

24 .94488 

25 .98425 

26 1.02362 or 1 inch 

Any millimeter measurement may be reduced to inches by 
multiplying by .03937. One centimeter equals .3937, or prac- 
tically four-tenths of an inch. One meter equals 39.37 inches, 
or 3.28 feet, or 1.094 yards. 



This is a subject second to none in importance. A very 
slight difference in the set of the carbons may make a very 
large difference in screen illumination, particularly when 
using A. C. 

Practically all illumination available for use comes from 
what is known as the "crater." With D. C. there is only 
one crater, but with A. C. there are two. The crater always 
forms on the positive carbon. With D. C. one carbon is 
always positive and the other always negative, therefore the 
entire force of the current is expended toward the forming 
of a crater of ample dimension on one carbon, the positive; 
hence it is imperative that the positive wire be connected 
to the upper carbon. As has been said, the crater always 
forms on the positive carbon, but, remembering that with A. 
C. each carbon is alternately positive and negative many 
times each second, we readily see that a crater will be 
formed on both carbons, since both are positive half the 
time. It therefore follows that if the crater-forming force of 
the current is divided between two carbons, the craters will 
be much smaller than if an equal amperage of D. C. were 
used, the entire energy of which would be directed toward 
forming one crater. 

The light giving power depends upon (a) the temperature 
of the crater; (b) its area; (c) the character of the carbon. 
The temperature of the electric arc has, so far as I know, 
never been actually measured. It has, however, been esti- 
mated as high as 8000 degress C. I do not know, but it is the 
natural inference that, since the force of A. C. is divided 
between two craters, and the full force directed to one crater 
with D. C., the temperature of the D. C. crater would be 
higher, assuming the amperage in each to be equal. Be this 
as it may, however, with equal amperage the A. C. crater 
is very much smaller than the D. C. crater, nor is the com- 
bined area of the crater on both upper and lower A. C. 
carbons equal to the area of the single D. C. crater, where 
equal amperage is used. See Limit of Amperage, Page 292. 

Taking all these facts into consideration, it will be seen 
that it is very doubtful whether 40 amperes A. C. would 
produce a total candle power equal to that produced by 40 
amperes D. C., but, laying that question aside, and even al- 
lowing the candle power would be equal, the fact still remains 
that it is utterly impossible to utilize nearly so great a por- 
tion of the alternating current illumination for projection 
purposes as can be utilized when using D. C. Referring to 


Fig. 123, Page 295, and Fig. 124, Page 297, this is made clear 
by the examination of sketch C in both figures, which in 
both instances illustrates an ideal crater condition, one D. C. 
and one A. C. It will be observed that at B, Fig. 123, the 
crater is of ample dimensions, facing the lens in such manner 
that the strongest light hits pretty nearly the center of the 
condensing lens. In sketch C, Fig. 124, the crater sets at 
more of an angle to the lens; also it is very much smaller. 
The result of all this is that 

While it is possible to secure just as brilliant an illumina- 
tion with A. C. as with D. C. it will require practically double 
the amperage to do so. In other words, it will take close to 80 
ampere A. C. to produce a screen illumination equal to that 
produced by 40 amperes D. C. 

Operators will note that when the carbon tips are cold 
they may be brought very close together without any effect. 
They must, in fact, be brought into actual contact before 
there is any result. It will also be noted that although the 
carbon tips may be separated from one-quarter inch to three- 
eighths inch when the arc is burning normally, if the switch 
be opened, thus breaking the arc, and be immediately closed 
again, the current will leap the gap and the arc will reset 
itself between the still incandescent carbon points. This 
phenomenon is due to the fact that the carbon is volatized 
(transformed into a gaseous vapor) by the tremendous heat 
of the arc, and this vapor in itself forms an electrial con- 
ductor, though one of tolerably high resistance, while the 
air itself is a very poor conductor of electricity in fact an 
insulator. When the carbons are cold, or only red, they are 
not being volatized; therefore the vapor (often referred to 
as the "arc stream") is not present; there is only air between 
the carbon tips, and air presents too great a resistance to 
allow the current to leap from one carbon point to the other, 
even when the tips are very close together. For one, two 
or maybe three seconds after the arc is shut off, however, 
the carbon still continues to be volatized, and, therefore, the 
vapor is present, and the space between the carbon tips still 
bridged by the gaseous conducting medium. 

The commonly accepted explanation of the formation of 
the crater on the carbon tip is that minute particles are torn 
away from the positive carbon by the current. These par- 
ticles are mostly volatized as soon as they are torn off, 
though some of them- reach and are deposited on the nega- 
tive carbon tip, only to be volatized there later. The writer 


does not pretend to vouch for the correctness of this theory. 
It is given for what it is worth. 

Limit of Amperage. As previously stated, the larger a 
crater of given temperature the more light will emanate there- 
from. See computing C. P. of arc, Page 293. There is, how- 
ever, an economic limit to possible light gain through increased 
size of crater, if the light must be passed through a 4^ inch 
diameter projection machine condensing lens system. The 
theoretical light source to work in perfect accord with the 
optical principle involved in a lens system is a pinpoint, 
meaning a light the size of the point of a pin. As the area of 
the light source increases, the ability of the lens system to 
utilize the light is rapidly decreased, until a point is reached 
where any further gain of light through increase of area of 
the light source is only made at heavy expense. More than 
three years ago I said that this point was reached when the 
crater becomes one-half inch in diameter. I am still con- 
vinced that that statement is approximately correct. See 
"Matching the Lens System," Page 113; for further explana- 
tion and. data, also see Amperage, Page 157. 

This means that the economic limit of light for projection 
purposes lies between 50 and 60 amperes D. C., and between 
80 and 100 A. C., because the 60 ampere D. C. crater will 
be fully one-half inch in length by almost that in width; 
therefore any further increase in amperage will, if my theory 
is correct, be of comparatively slight value. 

I believe it is safe to say that beyond 60 amperes D. C., and 
perhaps 90 A. C., not more than 25 per cent, of the energy ex- 
pended will appear on the screen in the shape of illumination. 

A projection arc must be operated with the carbon tips a 
certain given distance apart, in order to obtain the best 
results, and this distance will vary according to the number 
of amperes used, the size of the carbons, etc. It follows, 
therefore, that, inasmuch as the carbon tips of a hand-fed 
projection lamp cannot be kept precisely the same distance 
apart constantly and under all conditions, the arc voltage 
will vary. Arc voltage is the pressure necessary to force 
the current across the space between the carbon tips. 

This equals the reading of the voltmeter when it is attached 
to the upper and lower carbon arms when the arc is adjusted 
.for perfect screen illumination. It is, however, the number 
of amperes flowing, not the voltage, which determines the 
size of the crater, hence the amount of light it will produce 


In this connection let us pause and consider the C. P. of 
the crater. It has been discovered by experiment that the 
brilliancy of the positive carbon crater is practically con- 
stant, regardless of amperage consumed, at approximately 
158 C. P. per square millimeter where solid carbons are 
used, and 130 C. P. where cored carbons are used. We are 
not interested in solid carbons, but for cored carbons this 
would mean a total crater brilliancy of 130 muliplied by the 
square millimeter area of the crater. This figures out at 
41,860 C. P. for a crater having an area of V-2. square mch.^ 

From this it will be seen that increased amperage gives in- 
creased illumination at the rate of 130 C. P. for each square 
millimeter of additional area of crater. 

It will also be seen that, the spot being a magnified image of 
the crater, it is highly important^that our condenser arrangement 
be such that the spot be given its normal diameter without 
withdrawing the arc from the lens beyond the distance absolutely 
necessary to prevent breakage. 

By the use of the foregoing the operator will be able by 
estimating the area of his crater in fractions of a square 
inch, or in millimeters, to compute the C. P. of his projec- 
tion arc with a considerable degree of accuracy. 

Simon Henry Gage and Henry Phelps Gage, Cornell Uni- 
versity, have conducted experiments with D. C. regular carbon 
sets which resulted as follows (See their "Optical Projec- 
tion") : Using direct current and regular carbon set, as per 
Fig. 123, a 15 ampere, 50 volt arc, taking current through a 
rheostat, consuming 750 watts in the lamp and 1650 watts in 
total gives a total C. P. of 3490, or 4.65 C. P. per watt consumed 
in the arc, or 2.12 C. P. per total watt consumed in the arc 
and rheostat. A 40 ampere, 51 volt arc, taking current 
through a rheostat consumes 2040 watts in an arc or 4400 
watts in total, and gives 12350 C. P., which is 6.05 C. P. per 
watt consumed in the arc, or 2.8 C. P. per watt consumed in 
both the arc and resistance. 

It will be observed from this that as the amperage in- 
creases, voltage remaining essentially the same, the light 
giving power per watt becomes considerably greater. At 
40 amperes there is a gain of 1.4 C. P. per watt of energy 
expended in the arc, and .68 of a C. P. per watt expended 
in the combined arc and rheostat, as against. the 15 ampere 

In these experiments it was shown that a mercury arc recti- 
fier, using 40 amperes at 52 volts, same carbon set, gave 
12150 C. P., a decrease of 200 C. P. as against direct current 



from a generator taken through a rheostat, which seems to 
indicate that the loss by reason of pulsations of the rectifier 
is almost negligible. With A. C., same carbon set, 40 am- 
peres with 27 volts at the arc gave 1830 C. P., or 2.42 C. P. 
per watt expended in the arc, or .70 of a C. P. per watt of 
total energy expended in the arc and rheostat, or 2.32 C. P. 
per watt of total energy expended in the arc and transformer 

Experiments have proved that there is but little difference 
in actual cost per C. P. in light from an alternating current 
arc taking current through a well designed transformer (econ- 
omizer) and D. C. 
through a rheostat, 
though the A. C. is 
much less satisfactory 
to use from any and 
every point of view. 

"Optical Projection," 
by Simon Henry and 
Henry Phelps Gage, 
gives the following ex- 
cellent chart of rela- 
tion between power 
consumption and candle 
power. By this chart it 
will be seen that for the 
power consumed, A. C. 
through a rheostat gives 
the least per watt; D. C. 
through a rheostat next; 
A. C. through an econ- 
omizer next, and A. C. 
through a rectifier best 
of all, but the chart is 
presumably plotted for 

a 110 volt supply, taking no account of a lower voltage supply. 
The upper left hand line shows that if only the actual power 
consumed in the arc itself be considered, then D. C. has 
much the greater efficiency. Well, I am not good at plotting 
curves, but if .we consider a 60 or 70 volt D. C. supply, such 
as most isolated light plants used by theatres deliver, then 
D. C. through a rheostat ought to have an efficiency fully 
equal to the rectifier current, or possibly even of considerable 
greater efficiency. 









L x 


















Power Consumed 






4 L 




v '>*'' 
















Figure 122. 



This is a little digression from the main subject, which we 
will now resume. 

Position of the Crater. In considering light for projec- 
tion, however, the foregoing must be coupled with another 
item of prime importance, viz., the position of the crater. 

This latter is the most important point of all, since no 
matter what amount of light the arc may be producing, if 
that light be not directed toward the lens, then a large pro- 
portion of it or even perhaps practically all of of it will be 

Figure 123. 

wasted. If the crater points downward, the greater per- 
centage of light will be thrown in that direction, as is 
illustrated at A, Fig. 123, in which the strongest light would 
follow line X, and only a very slight percentage reach the 
lens, as indicated by the lines. Such a setting would be 
enormously inefficient. 

For best results the crater must be exactly in line with 
the optical axis (center) of the condensing lens. Inasmuch 
as all the light comes from the crater, it therefore follows 
that the more squarely the crater can be made to face 
the condensing lens, without causing the lower carbon tip 
to interfere too much in the light ray, the greater percentage 
of light will reach the lens, and be made available for pro- 
jection. This is illustrated in Fig. 123, in which A shows 


a highly inefficient D. C. setting; B a setting somewhat more 
efficient, but still not a good one because the crater points 
too much downward, and the strongest light would follow 
line, X, thus missing the lens entirely. C, however, is an 
ideal condition that is to say, the ideal practical condition, 
since, for certain reasons well understood by operators, it is 
impossible to get a good crater and have it squarely face 
the lens, so as to cause the strongest light to pass exactly 
through the center of the lens. Assuming the amperage of 
arcs A, B, C, Fig. 123, to be equal, each arc would give off 
practically the same amount of light, but that of A and B, 
being misdirected, would not illuminate the screen nearly so 
brilliantly as would the light from C. 

The position of the crater is controlled by (a) the angle of 
the lamp and (b) the relation of the carbons to each other. 
The condition at A is the result of setting the carbon tips 
central with each other, as per 1, Fig. 123; B is the result 
of advancing the lower carbon tip slightly ahead (toward the 
lens) of the upper carbon tip, as per 2, Fig. 123; C is the 
result of advancing the lower carbon slightly more than at 
3, as per Fig. 123. This, however, can be overdone, as is 
shown at D, Fig. 123. At D both the angle of the lamp and the 
advancement of the lower carbon is too great, the result being 
that, while we have a crater facing the lens squarely, still the 
advantage thus gained is neutralized by the fact that the 
lower carbon tip comes between the crater and the lens; 
also at Z a long skirt has formed, due to the fact that the 
lower carbon has been advanced too far. This form of 
crater is in itself inefficient, and, moreover, when the arc is 
shut off and the carbon is allowed to cool the skirt is apt 
to break off about midway of the crater, thus utterly ruining 
the crater and very seriously injuring the illumination until 
a new one is formed. 

Re-examining C, Fig. 123, we observe that the lower car- 
bon tip begins to interfere in the light at the fourth line 
down, but that the lower line from the lens to the crater 
misses the carbon tips and strikes the crater above its center. 
This is about as good a condition as you can hope to obtain. 
These sketches are not designed to accurately portray actual 
arc conditions exactly as they are, but merely to set forth, 
in understandable form, the various equations which enter 
into the matter of carbon setting, the faults which must be 
studied and guarded against, and to illustrate the best obtain- 
able condition, which the operator should strive to attain. 



When we consider the alternating current arc, however, 
we encounter an entirely and a radically different propo- 
sition; also one which is more difficult to handle where 
less than 70 amperes are used. As already explained, the 
crater will form on both carbon tips when A. C. is used, since 
each carbon is alternately positive and negative many times 
each second. As has already been set forth, the amount of 
available projection light will, within certain limits, be in 
direct proportion to the area of the crater, how squarely it 
can be made to face the condenser, and kind of current. 
With the crater-producing force divided between two car- 
bons, as is the case with A. C., it follows that neither crater 
will be as large, for a given number of amperes, as would be 

Figure 124. 

the case with D. C., with which the whole crater making force 
is centered on one carbon. It is even true, as I have already 
said, that both A. C. craters combined will not equal the area 
of one D. C. crater, where equal amperage is used. 

It has long since been very generally accepted as a fact, 
however, that, due to optical difficulties, it is neither feasible 
nor good practice for operators projecting with A. C. to use both 
craters. Operators who study the details of projection have 
long since come to the conclusion that a more uniformly ex- 
cellent result will be had by using only one A. C. crater, the 
upper, of course. One effect which almost certainly follows an 
attempt to use both craters is a double spot at the aperture, 


with liability to produce a dark, or multicolored streak across 
the center of the screen. This is due to the fact that the spot 
is merely an image of the crater (see Page 130), and with two 
craters there will be two images, which are not superimposed 
upon each other. 

For years an effort was made to use both craters by means 
of what was known as the "jackknife" set, illustrated at B, 
Fig. 124, and A, Fig. 124. Some also attempted to utilize 
both craters by setting the lamp straight up and down, but 
these schemes have, for the most part, been relegated to the 
scrap heap, where they rightly belong, and today the b st 
men, men securing the best results and holding the best 
positions, almost invariably use practically exactly the same 
set (illustrated at C, Fig. 123, and in Fig. 126), both for A, 
C. and D. C., or else use a very modified jackknife set by 
setting the lower carbon so that it angles out very moderate- 
ly with relation to the rackbars, angling the top carbon to 
meet it, as in A, Fig. 124. Even this scheme has, however, been 
largely discarded in favor of the regular D. C. set. Years 
ago I advised, both in my books and in the Projection De- 
partment of the Moving Picture World, the use of the same 
set for A. C. and D. C. / still advise it. Theoretically, setting 
the lamp straight up and down is better; practically, however, 
it is not. By using the straight up and down lamp set, or the 
jackknife set, one is enabled to get considerably higher candle 
power through the lens for a given amperage. That is a con- 
ceded fact, but the fly in that particular box of ointment is 
that a steady light absolutely cannot be maintained with these 
sets, or, in other words, the curtain illumination cannot he held 
at uniform brilliancy. I cannot recommend either the setting 
of the lamp and carbons perpendicularly, the jackknife set, 
or any other set except that shown in Fig. 126, Page 300, 
known as the "regular D. C. set." 

At E, Fig. 124, we see the result of carrying an alternat- 
ing current arc too short the carbons too close together. 
The A. C. arc is very short much shorter than the D. C., 
and this fault must be carefully guarded against. The D. C. 
current arc of 40 amperes will be one-quarter inch to three- 
eighth inch in length; the A. C. arc of less than 60 amperes 
will not be much in excess of one-eighth inch. It is thus 
made plain that the operator has slight leeway in handling 
the A. C. arc. It must be watched very carefully, fed fre- 
quently, and not allowed to vary from normal length. The 
condition shown at C, Fig. 124, is as good as you can hope 
for when using 60 amperes or less. It can only be obtained 



Figure 125. 

by very careful adjust- A b 

ment of the carbons, 
and maintained by exer- 
cising watchful care. D 
shows a condition Where 
the lower carbon tip has 
been advanced a little 
too much with relation 
to the upper one, so that 
the front edge of the 
lower crater is built up 
until it shuts off a large 
portion of the light em- 
anating from! the upper 
crater. This condition, 
too, must be carefully 
guarded against. The 
only remedy for condi- 
tion E, Fig. 124, is to 
burn a long arc until the 
saw teeth are burned off. 
The only remedy for 
condition D, Fig. 124, is 
to alter the relation of 
the carbons by shoving 
the top carbon tip ahead 
slightly, or pulling the 
lower one back. 

When using D. C. the 
careless operator who 
allows his arc to become 
too short may find the 
tip of his lower carbon 
crowned with a sort of 
mushroom a cap having 
a slim stem. This cap 
is composed of graphite. 
It is caused by keeping 
the carbons too close 
together, so that the 
arc does not get sufficient 

air properly to volatize the carbon. Under these conditions 
the carbon particles carried from the crater are deposited 
on the top of the negative carbon in the form of graphite. 
Graphite has high resistance, and will withstand enormous 


temperature for a long time. Therefore, this cap or mush- 
room is consumed very slowly. The remedy is to knock it 
off with a screw-driver having an insulated handle, and to 
be careful not to again allow the arc to get so short. 

Side-Lining the Carbons. It is essential that the upper 
and lower carbons set exactly straight with each other, 
viewed from the front that is to say, through the condensing 
lens opening, as per A, Fig. 125, in which A shows correct 
lining; B, top carbon out of line and C both out of line. 

Modern lamps have an adjustment by which the carbon 
tips may be lined with each other sidewise, but if the upper 
and lower carbons be not in line with each other throughout 
their length then as they burn away a constant sidewise 
adjustment of the carbons will be necessary to keep; the 
crater from moving over to one side. 

When the operator takes 
charge of a plant, or when 

^gjjjjijjajk a new outfit is purchased, he 

should put in two carbons of 
equal diameter, line their 

Hfc tips exactly sidewise and 

wR then, with a straight edge 

wk laid against the side of the 

b two carbons, test them for 

Ik side line. If either carbon 

Rk is out of perpendicular he 

W| should carefully file the car- 

bon clamp until the matter 
^L. is remedied. It is no uncom- 

^k mon thing to find lamps with 

|^^^^ W| either the upper or lower 

H| Hk carbon, or perhaps both, out 

^L ... Hi of plumb sidewise. With 

8k Vk some lamps it is possible to 

9L remedy this matter by 

jlL loosening the screws which 

HL^^jjH hold the carbon arm and 

shifting the arm slightly. 

.JBHHKl-JLSL. At Fig. 126 is a photo- 

graphic representation of the 

Figure 126. set which I strongly recom- 

mend for both D. C. and A. C. 

In closing the subject of carbons let me impress upon your 
minds as strongly as possible the following: 


Only the best possible results from a given amperage can be 
had when the crater is in precisely the right position with rela- 
tion to the lenses, with the least possible interference by the 
lower carbon tip, and this condition can only be obtained by a 
very careful adjustment and setting of your carbons. 

Some interesting data and information may be found in the 
following tabulated results of experiments made by the 



Current Through G. E. 50 Ampere Mercury Arc Rectifier 
on Lowest Notch. 

Approximate distance between 

carbon tips at their nearest Voltage at 

point. Arc. Amperage. 

1/16" 40 33 

1/16" 45 28 

3/32" 50 2S*/ 2 

1/8 " 55 22y 2 

3/16" 60 20 

1/4 " Arc unstable. 65 

5/16" Arc very unstable. 70 15 

75 Arc went out. 


Approximate distance between 
carbon tips at their nearest Voltage at 

point. Arc. Amperage. 

1/32" 40 31 

3/32" 45 2?y 2 

3/16" 50 24*/ 2 

1/4 " 55 22^ 
5/16" 60 
3/8 " 7/16" 65 

70 Arc very unstable 

and went out after 

five seconds. 

It was observed that with two new five-eighth inch cored 
carbons, in order to keep the arc voltage down to 50, and 
thus keep the amperage within reasonable bounds, it was 
necessary to separate the carbons \% inches for the first 15 
to 30 seconds, after which the arc resistance gradually but 
rapidly rose, until a 50 volt, 25 ampere arc was had with as 
little as three-thirty-second inch separation at the nearest 



point of contact between the lower tip and the crater on 
the upper carbon. 

With a new set of the same size carbons, but with cored 
above and solid below, the extreme distance was reduced from 
1/4 inch to 1 inch, and the arc voltage reduced to normal 
much earlier than with two cored. 

After striking an arc with two new five-eighth inch cored, 
burning it 20 seconds, breaking it long enough to measure 
distance between tips, and relighting, with 30 volts across 
the arc there was still 50 amperes, and the arc was still 
abnormally long. Under similar conditions, with two cored 
and the arc voltage at 40, amperage stood at only 30. 

All this has some value in that it shows a less tendency 
to heavy current rush on new sets when a solid is used 

Carbon Economizers. There are now on the market a 
number of good carbon economizers, ranging in price from 
50 cents to $1 which may be had from supply dealers. These 
devices are designed to allow the operator to 'consume his 
carbon stubs down to the shortest possible length. Some 
are made of brass, and some of iron. 'They are simple and 
quite effective. 

Lighting Interior of Lamphouse. It would be a very 
simple matter to place a small porcelain lamp receptacle 

in the bottom of the 
lamphouse, at the right 
hand, front corner. From 
one side run a wire to one 
side of any convenient 
% incandescent circuit. From 
-o the other side attach to the 
~ other side of the circuit 
through a spring-switch, 
- made as per Fig. 127, at- 
tached to the right hand 
lamphouse wall in such 
way that a piece of fibre 
fastened to the lamphouse 

Figure 127. 

door will shove the switch open, thus putting out the light, 
when the lamphouse door is closed. 

By the use of a low C. P. lamp the interior of the lamp- 
house 'is thus automatically illuminated when one opens the 
door to re-set the carbons, etc. 


Arc Controller 

WHILE the Arc Controller is a new invention it has 
been in use long enough to thoroughly prove its 
practicability and utility; also it carries with it the 
indorsement of the Projection Department of the Moving Pic- 
ture World. 

The function of the controller is automatically to feed the 
carbons of the arc lamp. Its method of accomplishing this 
is quite simple and thoroughly positive. 

Plate 1, Figure 128. 

Broadly speaking, the amperage of the arc is regulated by 
the voltage of the arc, and no matter whether current be 
taken through a rheostat, directly from a generator, or 
through a transformer, any change in voltage across the arc 
will cause corresponding change in amperage at the arc. If the 
voltage rises the amperage drops; if the voltage drops, the 
amperage rises. This is what may be termed the immutable 
law of the electric arc. 


The Arc Controller operates as follows: In P. 1, A is a 
small motor which drives the mechanism of controller B, 
illustrated in P. 3. Controller B, P. 1, is connected to the arc 
lamp by means of rod 2, P. 1 and 2, this rod being driven by 
gear 44, P. 3. By tracing through the connection you will 
see that motor A is thus positively and directly connected 
to rod 1, P. 2, which is commonly known as the "feed 
handle" of the arc lamp the handle by means of which the 
carbons are fed together. Motor A, P. 1, is connected to 
the line by means of wires contained in cable 9, P. 1, the 
other end of which is seen at 7, P. 1, where it joins the 
fuse box. The motor is not connected directly to the 
supply line, but to the projection machine table switch 
contacts, through cables 8, P. 1, which are controlled by 
switch 5, P. 1. It will thus be seen that motor A does 
not receive the full line voltage, but only the arc voltage, 
which varies with the length of the arc. Now, even the 
novice will understand that the speed of motor A will depend 
upon the voltage of the current with which it is supplied, 
hence, any rise in arc voltage, no matter how small, will in- 
crease the motor's speed. 

Referring to P. 2, knurled knob 12 passes through fibre 
disc 9, through the end of brass lever 16, and impinges on 
the surface of fibre disc 8. 

Brass lever 16 is hinged to a steel collar, which passes 
over and is attached to feed rod 1, P. 2. Now, when knurled 
knob 12 is backed off (unscrewed somewhat), it has the 
effect of unlocking fibre disc 8 and driving gear 4, from 
fibre disc 9 and feed rod 1. In other words, when knob 12 
is loosened, or backed off, the lamp becomes a plain hand- 
fed lamp, of which fibre disc wheel 9 is the feeding knob or 
wheel, and the motor is allowed to drive gear 4 and fibre 
disc 8, without moving rod 1, P. 2. Conversely, when knurled 
knob 12 is screwed in the whole thing is locked together, and 
the motor then drives lamp feed rod 1, P. 2, direct, by means 
of gear 6 acting on gear 4, thus feeding the carbons of the 
lamp together. To make matters still more clear, gear 4 and 
fibre disc 8 merely use rod 1 as an axle. They are entirely 
independent of disc 9 and rod 1, except when locked to them 
by knurled knob 12. When not so locked, gear 4 and disc 
8 can rotate without in any way affecting disc 9 and rod 1. 
The operation of the device is as follows: When the operator 
is ready to strike his arc, he closes switch 5, P. 1, which 
starts motor A running, but it is only driving fibre disc 8 
and gear 4, P. 2. The operator now strikes his arc by means 



of the hand feed (disc 9, P. 2), in the usual way, adjusts it 
at approximately the right length, and then screws in knurled 
knob 12, which locks the mechanism together, and thereafter 
he theoretically need give the arc no further attention what- 
You will observe I said "theoretically"; this by reason of 

Plate 2, Figure 129. 

the fact that faults in the carbon and things of the sort may 
make it necessary occasionally to work the hand feed. As 
a general proposition, however, the controller takes care of 
the entire situation, so far as feeding of the carbons be con- 
cerned, and I have myself seen a full show of eight reels run 
without the operator at any time touching the arc lamp, ex- 



cept to strike and set the arc at the beginning of each reel. 
The controller maintains a perfectly steady arc voltage, 
hence a perfectly steady arc amperage and even light density. 

The Controller. P. 3 is an interior view of controller B, 
P. 1, with cap 1, P. 1, removed. In this view gear 10 is the 
gear which meshes with gear 44, P. 3, which drives rod 2, P. 1. 
Now follow me closely: Spring 41, P. 3, is attached to pawl 23 
by slipping bend 42 into the eyehole at 22 of part 23, P. 3. 

Plate 3, Figure 130. 

This has the effect, when cover 40 is in place, of holding 
part 23 back, in the direction of the arrow point 34. Parts 
28-28 are governor weights attached to governor cross bar 
27 by means of hinge pin 47 and 35, and right here is what 
might be termed the heart of the whole machine. Part 3? 
swivels upon part 32 and the whole governor is attached to 
the main driving shaft by pin 38 in part 27. Part 31 is a 
steel tooth driven through part 23, and protruding about 
one-eighth inch on the side next to wheel 16. All the parts 
between part 27 l /2, which is a ball bearing, and part 26, an- 


other ball bearing, which includes the entire governor, 
revolve at the speed of the motor, and weights 28-28 are 
held normally in, by means of spring 41 which holds part 
23 back against ball bearing 26, which in turn presses back 
part 32, carrying pins 25, which bear on the inner end of the 
arm carrying weights 28-28. Before going any further study 
this action closely, and get it firmly fixed in your mind. 

Now here is how the thing operates. The motor runs 
constantly, but its speed increases as the length of the arc 
increases, because the voltage increases with length of arc, 
and as a result of the increased motor speed, governor 
weights 28-28 are thrown outward against the pull of spring 
41, which has the effect of forcing part 32, ball bearing 26 
and part 23 ahead, thus engaging tooth 31 with one of stop 
teeth 15 on wheel 16. 

Gears 14-17-29 form a "differential," gear 29 being attached 
to wheel 16, gear 14 to shaft 19 (by means of pin 13), and gear 
17 to gear 18. Underneath gear 18 is a worm gear attached 
to the shaft connecting the controller to the motor the main 
driving shaft. This worm gear drives worm gear 18, mounted 
and riding loosely on shaft 19. When the motor is running, 
but the arc is not being fed, the motor continues to drive 
gear 18, but, wheel 16 being free to turn, the differential acts 
and gear 29 simply runs around on gear 13, without oper- 
ating gear 10. A moment's study will, I think, enable you 
to understand this action. It is very similar to the action of 
the differential of an automoble. Gear 29 must rotate gear 
10, which in turn drives gear 44 and rod 2, P. 1 and 2, and 
through it lamp feed handle 1, P. 2, thus feeding the lamp 
carbons together, shortening the arc and reducing the voltage 
so that the motor slows up, whereupon spring 41 overcomes 
the lessened centrifugal force acting on weights 28-28, so 
that they are pulled inward, which disengages tooth 31 from 
tooth 15, which causes the differential to act and the carbons 
are no longer fed. 

The speed necessary to cause tooth 31 to engage tooth 15 
will depend entirely upon the tension of spring 41, which is 
regulated by nut 46 on bolt 45, P. 3, (3, P. 1), and this tension 
must be adjusted by the operator as soon as he has the con- 
troller connected up, as will be hereinafter explained. 

Oil. The well formed by the gear casing should be kept 
filled with a good grade of dynamo oil. Oil is poured in 
through oil well 14, P. 1, and it should reach the level of the top 
of the spout. One filling of good lubricant ought to last about 


500 running hours. Before refilling, remove the plug in the 
opposite end of 14, P. 1, drain out all the old oil, replace the 
plug, fill the well with kerosene and let the machine run for 
a few minutes; drain the kerosene out and then refill with 
clean oil. 


/*>.? tf.^f 

*T"r~rv~r iv,<v*- 


Plate 4, Figure 131. 

Caution: You are cautioned against the use of the very 
thin, much advertised oils. They are totally unfit for use on 
such machines as this. The manufacturers of the controller rec- 
ommend Solar Red Oil. I do not personally know anything 
about this lubricant, but presume it is good. In any event, 
however, a good grade of dynamo oil will serve the purpose. 
If the Solar Red Oil can be had, use it; if not, use the other, 
which you can no doubt obtain from your local electric light 
company, or from any reliable oil dealer. 

Connecting the Machine. When a controller is received and 
unpacked, examine the packing carefully, making sure that no 
small parts are thrown away. Also remember that the manu- 
facturer will not recognize claims for shortage unless made 
immediately after receipt of the machine. The apparatus will con- 
sist of the following: (a) The controller and motor, con- 
nected in one unit, as shown in the lower 1 half of P. 1, 
including cables 7, 8, 9 and the fuse box as shown in P. 1. 
All this will be found coupled together when received: (b) 
telescope rod 2, P. 1 and 2, consisting of a steel rod inside 
a brass tube; (c) collar \ l /2, part 3, including gear 6, fork 7 
and universal joints 13, P. 2; (d) gear 4, fibre knobs 8 and 9 
and part 16. 

After unpacking and inspecting the parts proceed as fol- 
lows: First set the controller and motor, B-A, P. 1, on the 
floor immediately under the feed rod handle of the arc lamp. 
It may be set on a block high enough to raise it out of the 
dirt say 3 to 6 inches, if desired. If necessary the controller 
may be set a little to one side, or a little back, if the conduit 
carrying the lamp leads is in the way. Within the limits 



of the reach of telescopic rod 2-2, P. 1 and 2, the position of 
the controller may be changed The idea is shown in P. 7. 

Caution: In this connection be very careful not to get 
the controller so far away from a position underneath the 
lamp feed handle that universal joint 4, P. 1, and the univer- 
sal joint 13, P. 2, will be at too great an angle and bind. It 
is hardly probable that you would do this, but it is never- 
theless possible, and must be guarded against. 


) C) 


O () 



Plate 5, Figure 132. 

Having placed the controller, next take off the feed wheel, 
or knob, from the rod which feeds the carbons of your lamp, 
and slip collar 1J4, P. 2, on the rod. Now, take part 3, carry- 
ing gear 6 and fork 7, in your left hand, and gear 4 and fibre 
knobs 8 and 9 in your right hand, and fit them together so 
that gear 6 meshes properly with gear 4, and the hole through 
the hollow stem, 18, P. 2, is clear, except for the pin passing 
through it. Having fitted the parts together in your hand, 
slip the whole on rod 1, first having removed knob 17, P. 2, 
or the knob of some other rod which conies most directly 
under rod 1, and make fork 7 straddle the rod; after which 
knob 17 should be replaced. It may not be necessary to 
remove knob 17. Very likely you can get the fork over the 
rod without. The reason for fork 7 straddling one of these 
rods is to prevent part 3 from turning to hold it stationary. 



Slip these parts on rod 1 until its end strikes the pin which 
you will see in hole 18, about one-half inch from the surface 
of the fibre knob. This pin must not be removed. If the 
parts do not go on the rod easily do not try to force them 
but find out what is wrong and remedy it. Having accom- 
plished this, tighten up set screw 15, P. 2, good and tight. 
Bring back collar l l / 2 to about the thickness of a postal card 
from the sleeve inside part 3, and tighten its set screw. 

Now all you have to do is to connect rod 2, P. 1 and 4 with 
universal joints 4, P. 1, and 13, P. 2, and remove the wooden 
plug from the cover of the controller. Its use is to preserve 

Plate 6, Figure 133. 

in transit the oil with which the controller is filled. The hole 
that it protected is a "breather," and must be left open when 
the controller is in operation. 

If gear 6, P. 2, does not incline at the proper angle to clear 
rod 2 from any obstruction, loosen a screw on the right side 
of part 3 and, with knurled knob 12 loosened, turn gears 6 
and 4 and fibre knob 8 to the desired angle. Then tighten the 
screw in part 3 very tightly. This completes the mechanical 

Electrical Connections. First if your current is D. C. see 
to it that your rheostat is placed in the positive wire (the 
wire leading to the upper carbon), and between the machine 

table (operating) switch and the lamp. // it is on the negative 
wire change it to the positive, and then if the current is 110 or 



115 volts make your connections as per P. 4, in which A is 
the switch-box, shown photographically in P. 1, and dia- 
grammatically in P. 5. On the leads from switch-box A will 
be found tags reading respectively "field," "line," "armature," 
the field and line wires being in the same B-X conduit. The 
field wire must be connected to the positive pole of the ma- 
chine table or operating switch, on its dead side, at B, P. 4. The 

Plate 7, Figure 134. 

line wire must be connected to the opposite pole, at C, P. 4. 
The armature wire, which is asbestos covered, must be con- 
nected to the positive asbestos covered lamp lead (one leading 
to upper carbon), between the rheostat and lamp, as per P. 
4. This may be done by removing the insulation of the lamp 
lead for an inch or so, scraping the wire strands and the end of 
the armature wire perfectly clean, wrapping the end of the 
armature wire tightly around the lamp lead and soldering 
the joint, after which the joint must be wrapped with in- 
insulating tape. It is VERY IMPORTANT that all the electrical con- 
nections be perfectly tight. 


P. 5 shows the wiring of switch-box A, P. 4, and 6, P. 1. 
The B-X conduit joining the switch-box and the motor A, 
P. 1, contains three No. 14 wires, each having a different 
colored insulation, one red, one white and one black. The 
red is the field wire which connects through the switch-box, 
to B, P. 4; the white wire is the line which connects at C, 
P. 4, and the black the armature, which emerges from the 
switch-box as an asbestos covered wire. The connections 
are perfectly plain when you, in your mind, substitute P. 5 
for switch-box A, P. 4. 

Caution. Be very sure that your rheostat is located on the 
SWITCH AND THE LAMP. If it is on the other (line side) of the 
machine table switch, change it, since otherwise the con- 
troller would not work. 

It is, however, possible to have the rheostat in the nega- 
tive wire or on the other side of the operating switch by 
using different wiring diagrams, and the manufacturers pro- 
vide for this if notified, but the simplest way is to use one 
diagram and change the position of your rheostat if neces- 

When using converted alternating current, through a motor 
generator set, rotary converter, or mercury arc rectifier, 
or where D. C. voltage is reduced by D. C. to D. C. econ- 
omizer, the wiring diagram as per P. 6 must be used, though 
it applies to no other condition. 

In ordering the controller you should send an exact dia- 
gram of your wiring, decribe, in detail, the various apparatus 
used, and give the kind of current and its voltage, and, if A. 
C., the cycle. In using diagram, P. 6, if there is an arrange- 
ment for switching over to A. C. in case of failure of con- 
verting apparatus, then the controller connections must be on the 
converter side of a double-throw switch which will cut it out 
of service when A. C. is used, because under no circumstances 
must the controller be subjected to alternating current, or any 
voltage higher than 115. 

Operation. The controller will maintain the length of arc 
for which it is adjusted, and the length of the arc is altered 
by tightening or loosening nut 46, P. 3. After the controller 
has been connected up and put into operation, if the arc is 
too short, tighten up on this nut; if it is too long loosen it 
until the desired length is attached. Examine the oil cups of 
the motor once a week and fill them up. Examine the com- 
mutator of the motor occasionally. 


Should anything go wrong with the internal gearing of the 
controller it will be necessary that it be returned to the factory 
for adjustment. It is not advisable to try to repair the con- 
troller yourself, but, on the other hand, it is extremely im- 
probable that anything will go wrong. 

Use only motor brushes supplied by the manufacturers. 
The motor brushes may be removed by unscrewing their 
brass retaining disc, but in replacing be sure they are exactly 
in the position from which they were withdrawn. The 
manufacturers show one pencil mark on the top of the left-hand 
brush and two pencil marks on the top of the right-hand brush to 
indicate their correct positions. The box in the top of the 
motor is merely a junction box in which the leads from the 
motor are soldered to those in the B-X leading therefrom. 


The connection between the machine table switch and the 
arc lamp and between the machine table switch and the 
rheostat invariably is made with what is called asbestos- 
covered strand wire, this by reason of the fact it must be 
quite flexible; also, its insulation must withstand consider- 
able heat. 

Following the recommendations of the Projection Depart- 
ment! of the Moving Picture World and the Handbook the 
general practice is to use No. 6 asbestos wire, and this size 
is ample for ordinary work. However, everything con- 
sidered, I believe that in houses where high amperage is 
used it would be good practice, and true economy in the end, 
to use No. 5 instead of No. 6 abestos wire. No. 6 is more 
than capable of carrying the current, it is true, but portions 
of it are subjected to pretty high temperature, so that, on the 
whole, while granting that No. 6 will answer, I believe No. 

5 would be still better. 

Before asbestos strand wire is purchased a sample, which 
may be only half an inch long, should first be secured and the 
diameter of a few of the strands, picked out at random, 
carefully measured in thousandths of an inch, with a mi- 
crometer caliper. Having done this you can look at Table 

6 and see what number of wire the strands are. Next 
multiply the diameter by itself, which will give you the 
C. M. cross-section; count the number of strands in the wire, 
and multiply the area of one strand by the total number of 
strands, which will give you the total C. M. cross-section 



of the sample. Compare this with area of the wire it is 
supposed to be and if there is a discrepancy on the wrong 
side don't buy the wire, but demand one having such number 
of strands that their combined cross-section will equal the 
cross-section of this size wire you want. This is important, 
because many manufacturers of stranded wire, depending 
upon the carelessness or ignorance of the purchaser, hold 
out from five to ten strands. Only a vigorous, combined 
kick will stop this practice. 

Operators should watch their asbestos wire closely, and as 
soon as that portion inside the lamphouse begins to feel 
"soft" and pliable, without any spring to it, the end should 
be cut off and thrown away, since it has high resistance, and 
in a day's run will waste more power than it is worth. See 
Page 233 for a suggestion on this latter. 

Diameter of Small Wires. 

B. & S. Gauge. 

Diameter in Decimal 
Fractions of an Inch. 

Diameter in Mills. 














































Note: Mill diameter is not exact. 


Toledo Non-Rewind 

THE Toledo non-rewind includes an aluminum cast maga- 
zine, 5 inches deep by approximately 16 inches in diameter, 
upon the back of which is mounted an intermittently run- 
ning motor which drives a mechanism carrying reel A, 
plate 1. This reel is specially designed. Its hub is col- 
lapsible, being controlled by lever 1 and' spring 2. Mounted 

Plate 1, Figure 135. 

on a circular metal plate 3, to which the reel is attached 
when in the magazine, is a collapsible metal band, not 
visible in the photograph but controlled by knob 4, P. 1. 
The operation is essentially as follows: 

When the reel is received from the exchange it is placed 
in the magazine on an extension to spindle 5, and the mag- 



azine is, by a suitable mechanism, shown at X in P. 2, re- 
leased and swung half way around, whereupon the film may 
be threaded through the magazine the same as it would be 
were the regular upper magazine in use, a non-rewind reel 
meanwhile having been placed in the lower magazine to 
receive the film. After the film is wound on the non-rewind 

Plate 2, Figure 136. 

reel the operation from then on is simple. The non-rewind 
reel is placed in the upper magazine, and the mechanism 
is, by a few simple moves, adjusted, locking the reel to the 
back plate which is driven by the motor on the back of the 
magazine, P. 2. After locking the reel into place, the col- 
lapsible band is, by the movement of a lever, brought down 



until it clamps the outer circumference of the film. This 
band expands and contracts in a true circle, and will accom- 
modate a reel of film as small as 450 feet or as large as 1100 

It is somewhat difficult to describe the action of this 
machine without an abundance of carefully numbered photo- 
graphs, which, as the Toledo was only placed on the market 
at about the time this book was ready for publication, there 

Plate 3, Figure 137. 

was not time to prepare. However, the motor shown in P. 2 
is controlled by switch B, P. 2, and this switch in turn is 
actuated by a roller which bears upon the film at X, P. 1. 
When the length of film shown in P. 1 is drawn taut this 
roller is shoved back, which raises switch B, P. 2, thus making 
electrical contact and starting the motor. When the motor 
is running, the reel in the upper magazine is revolved, which 
has the effect of releasing a portion of the film and literally 
shoving it out of the reel. The instant this is done, the 


length of film shown in plate 1 slacks, which lets the roller 
go forward, thus opening switch B, P. 2. As a matter of 
fact, in actual operation the motor starts and stops about 
twice every second. 

As will be seen the film is taken from the center of the 
reel. It is brought out across an angle piece and comes 
down through a firetrap, into the mechanism, through which 
it is threaded in the usual way. The power required, so far 
as wattage be concerned, is almost nothing. It would prob- 
ably not add more than 25 cents to the current bill in a whole 
month, if it does that much. 

P. 1 and 2 show the front and back views, and P. 3 the 
magazine turned to receive the exchange reel on the first 
run. With this device it is not necessary to do any rewind- 
ing at all. 


Feaster Non-Rewind Machine 

HIS device is a highly practical mechanism by means 
of which the rewinding of film is eliminated, except 
that it is necessary for the operator in the first place 

Plate 1, Figure 138. 

to wind the film from the exchange reel to a special reel, 
which is a part of this outfit. It can be attached to any 
machine by the average operator in just a few minutes. 


The magazines, 20-21, Plate 1, set level, regardless of the 
angle at which the projector mechanism may set. There 
are few parts to wear out, and any film in condition to go 

Plate 2, Figure 139. 

through a projector will successfully pass through the 
Feaster. In P. 1 and 2 the device is seen attached to a 
Power's mechanism. It attaches with equal facility to any 
standard projection machine. 

In attaching the Feaster to a Power's machine all that is 
necessary is to remove the upper magazine and replace it 
with the Feaster, -adjusting it with thumb screws provided 
until gear 7, P. 1, meshes properly with the gear on the pro- 
jector. Whereupon tighten up thumb screws, 3, P. 2, and 
level the magazines by means of turn-buckle 16, P. 2. This 
whole operation should not consume more than five min- 
utes. Attachment to other makes of machine is almost 
equally simple. The added complication in threading amounts 
to very little. 

Plate 2 shows the method of placing the film in the 
magazine. The film is first rewound from the exchange 
reel to a special Fenston reel, enough of which are fur- 
nished to carry any show. One side of the reel is instantly 



detachable. The threading is quite simple and sprocket, 
41, P. 3, maintains a constant supply of film to the mechan- 
ism, between Which and sprocket 41, inside the magazine, 

Plate 3, Figure 140. 

there is a loop as per P. 4. P. 4 shows the internal con- 
struction. Pan 31, which carries the film roll, rides on 
steel balls (three of them), 52, which are held equidistant 
from each other by ring 32. The friction is thus reduced 
to a negligible quantity. 



This or similar machines are to be commended for several 
reasons, not the least of which is that in many houses 
where the operator has been required to do the rewinding, 
he will be given just that much additional time to attend 
to his projection, and thus the show will be benefited. The 

Plate 4, Figure 141. 

most important reason for recommending these machines, 
however, is that their general use will very largely decrease 
the damage done to film. 



Resistance as Applied to the 
Projection Circuit 

RESISTANCE as applied to the projection circuit is 
no different in principle from resistance applied to 
any other circuit, but it will, nevertheless, I think, be 
advisable to give somewhat extended explanation of various 
points, since the element of variable resistance enters very 
largely into the matter. 

As a rule the voltage of the supply is a fixed quantity, 
which may be anything from 60 volts to, in extreme cases, 
500, but ordinarily is either 60, 70, 110, or 220. 

The requisite amperage is an extremely variable quantity, 
ranging from as low as . 12 for stereopticon projection to, 
in extreme cases, as high as 80, or even 90 in the projection 
of moving pictures. As a general proposition, however, 
amperage requirement for moving picture projection will 
range from 25 to 50 D. C, and from 40 to 60 A. C, though 
much more than 60 amperes A. C. ought ordinarially to be 

Figure 142. 

Now with a fixed voltage, 100 for example, the amperage 
will depend upon the resistance encountered. Having first 
carefully read and considered the text matter under "Re- 
sistance," Page 34, let us examine the resistance of the pro- 
jection circuit, laying aside, however, the resistance of the 
line and carbons, which is, in itself, a small quantity, usually 
ignored when figuring projection circuit resistance. 


If we were to connect a projection lamp to the supply lines 
as indicated at A, Fig. 142, when the carbons were brought 
together a dead short circuit would be established, which 
would instantly blow a fuse. To avoid this we establish 
resistance in the form of a "rehostat," as at C, sketch B, 
Fig. 142. This resistance operates precisely the same as 
does the resistance in the filament of an incandescent lamp. 
It only allows a certain given amperage to pass, the am- 
perage being dependent upon the voltage and the number of 
ohms resistance contained in resistance C. 

But right here another equation enters. The foregoing is 
true only so long as the carbons remain in contact with each 
other. The instant they are separated an arc is struck, and 
additional resistance is established in the arc itself, the 
amount of which will vary somewhat with the amperage, 
but more largely with the distance the carbons are separated 
from each other. However, in picture projection it is found 
that, with a given amperage, there is one certain distance at 
which the carbons must be separated from each other in 
order to secure the best possible projection light, and this 
distance cannot be allowed to vary appreciably without 
injuring the illumination of the screen, nor does the resist- 
ance vary to any large extent with ordinary differences in 
amperage. Therefore the resistance of the D. C. arc, when 
it is handled properly, will only vary between 45 and 55 
volts, seldom exceeding the latter quantity when operating 
at its best, and that of the A. C. arc of ordinary amperage, 
say up to 60, between 30 and 38. 

In the second edition of my Handbook I selected 48 as 
the figure fairly representing the voltage of the average 
D. C. projection arc. I see no reason to change that figure; 
therefore we will continue to consider the projection arc as 
having a voltage of 48, with the qualification that this is 
subject to variation between 45 and 55. In the same book 
I selected 33 as representing the average voltage of the 
A. C. arc. I think, however, in that case 35 is probably 
more nearly representative than 33, therefore I will now 
change my estimate of the average voltage of the A. C. arc 
from 33 to 35, and consider it as having a voltage of 35 in 
the future, understanding, however, as with the D. C. arc, 
it is a variable quantity, 35 being designed to represent the 

Now, having fixed all this clearly in our minds, let us 
proceed a little further. The supply voltage is, as has been 
said, fixed, meaning that each theatre is supplied with cur- 



rent at a certain given pressure, say 110 volts. One theatre 
may, however, require 35 amperes D. C. and another 45. 
How is each requirement to be met, when both have a 
110 volt supply? 

The answer is simple. Merely by varying the amount of 
resistance in rheostat C, sketch B, Fig. 142. It is also 
possible that only 12 or 15 amperes may be required at the 
stereopticon lamp, which simply calls for additional resistance 
in rheostat C, sketch B, Fig. 142. 

It is not only possible, but it is common practice so to 
arrange resistance that the amperage may instantly be 
varied at the arc merely by moving the lever of a dial 
switch. This is accomplished by what is known as an 
adjustable rheostat, the principle of which is illustrated in 
Fig. 143, in which A-B are supply lines, the rheostat in this 

Figure 143. 

instance being connected into line B. Line B connects to 
lever 6, which is the arm or lever of the dial switch, 1, 2, 
3, 4 and 5 being its contacts. With the lever on contact 5, 
as shown in Fig. 143, it will be readily seen that the current 
must pass through the entire eight coils of the rheostat, 
therefore with the lever on contact 5 the rheostat is supply- 
ing all the resistance it is capable of. If, however, we move 
the lever to contact 4, it will be seen that the current will 
pass down the wire and enter the resistance at the bottom 
of coil a, thus eliminating that coil, and, of course, its 
resistance, which increases the amperage accordingly. On 
the other hand, if lever 6 be on contact 3 then the resis- 
tance of two coils will be eliminated; if it be on contact 2, 
three coils will be eliminated, and if on contact 1, four coils 
will be put out of business, and we will then only have the 


resistance of coils e, f, g, and h, which forms what is known 
as the "fixed resistance" of an adjustable rheostat. 

The fixed resistance of the adjustable rheostat must always 
be sufficient to prevent enough current passing to overload 
the wires or grids composing the fixed resistance. 

This, I think, ought to make the action of the adjustable 
rheostat fairly clear. The same thing is seen photograph- 
ically illustrated on Page 338, Figs. 151 and 152. 

Other rheostats called "fixed resistance" rheostats have no 
dial switch. Their resistance cannot be varied without 
removing the casing and making a special connection. Still 
other rheostats are built of cells, each cell being a complete 
rheostat, containing a fixed amount of resistance. Each' one 
of these cells may be combined with the other cells, either 
in series or multiple, as will be. hereinafter explaind, so that 
the operator may vary the amperage by changing the con- 

In considering Fig. 143, if all the variable resistance is 
"cut out," leaving only the fixed resistance to oppose the 
voltage, and the coils or grids in the fixed resistance become 
red hot, then either the rheostat is not well designed, or 
else it is being used on current of higher voltage than it was 
intended for. A rheostat will do the work even though its 
coils or grids get red hot, but if worked under these con- 
ditions the life of its coils or grids will be very greatly 
shortened, and the heat may at any time become such that 
the metal will be burned in two (fused), thus stopping all 
current flow. 

It is a very good plan to have a few extra rheostat coils, 
or grids on hand, so that repairs may be made by the 
operator in case a coil or grid burn in two. Making such 
repairs ,is a comparatively simple operation, requiring only 
a fund of good judgment and horse sense, remembering 
always that it is absolutely essential that all coils or grids be 
thoroughly insulated from the frame and casing. 

Remember that,- no matter what the form of your rheostat 
may be, whether round, rectangular or square, whether of 
fixed or variable resistance, Whether of coils or iron grids, 
its electrical action is .always exactly the same. The 
current enters at one end of a series of coils or grids, passes 
through each coil or grid and loses a portion of its voltage 
in the process of overcoming the resistance. 

One point puzzles many very good operators, viz.: the 
voltage of the arc varies comparatively but little, and if it 


be true that the voltage is reduced according to the amount 
of resistance in the rheostat, why is not the arc voltage 
varied more greatly when a portion of that resistance is cut 
in or cut out of the rheostat? 

This is by reason of the fact that the increased or de- 
creased flow of current through eliminating a portion of the 
resistance, or adding resistance, automatically takes care of 
the matter, though it is true, as has been said, there is 
some fluctuation in the arc voltage when the amperage is 
changed. The whole question of resistance as applied to 
the projection arc is complicated. Results depend upon so 
many different things that it is quite difficult to arrive at a 
complete and clear understanding of the thing as a whole. 
We know how it works and what will be the result of the 
various things we may do, but it is sometimes rather diffi- 
cult to enter into detailed explanation of the exact why and 
wherefore of these results. 

Always thoroughly insulate your .rheostats, either by plac- 
ing on asbestos, slate,, marble, or some other heat-resisting 
insulating material. It is always possible that one of the 
coils of a wire coil rheostat will sag and touch the casing. 
If the rheostat itself be thoroughly insulated from the 
ground no immediate harm will be done, always provided 
no other coil does the same thing, but if this happens and 
the rheostat be grounded there is likely to be a blown fuse. 

It is also possible that a coil may sag against the casing, 
but not form sufficient contact to allow of anything more 
than slow current leakage. This may not cause the fuses 
to blow, but will nevertheless cause constant loss of power, 
and that loss will be registered on the meter. I have known 
of instances where managers have complained of excessive 
current bills, only to finally discover it was due wholly and 
entirely to this kind of leakage, Not enough current flowed 
to cause excessive heating, or to affect the fuses, therefore 
the operator had no suspicion of the existence of the fault. 

Never place rheostats on an iron covered shelf, or on other 
current-carrying material likely to produce a ground should 
the casing or frame of the rheostat become charged with cur- 
rent. Always place them on insulating material. 

Temporary Rheostat Repairs. If a coil of the rheostat 
should burn out and you have no other coil at hand, tem- 
porary repairs may be made as per Fig. 137, in which the 
dotted line represents the defective coil, and the black line 



a No. 6 copper wire, doubled, which has the effect of elimina- 
ting one coil. This kind of repair will work all right until 
a new coil can be procured and installed. You may also 
procure soft iron, from any hardware store, size No 8 
(diameter .128 of an inch), and make a temporary coil which 
may be installed in place of the defective one; such a coil 
will work all right for a time. The wire may be wound 
into a coil by using a mandrill of proper size set in a lathe, 
or you may wind it by using a piece of ^ or J^ inch gas 
pipe, or even a broom handle. Attach one end of the wire to 
the pipe, or whatever you use for a mandrill, and the other 
to some fixed object, backing away the length of the wire 
and rolling the mandrill while you pull on -it, thus rolling the 
wire on the mandrill in a close spiral, which must be stretched 

Figure 144. 

slightly endwise when installing, so that the spirals will not 
touch one another. There must be not less than 1/16 and 
preferably 1/8 inch between each spiral when the coil is 
installed. In installing a coil be very certain it is thoroughly 
and completely insulated from the frame of the rheostat.' 

Locating the Rheostat. Under no circumstances should 
a rheostat be placed within less than one foot of any wall 
containing inflammable material, unless there be a sheet of 
H inch asbestos between it and the wall, with at least a 1 
inch air space between the asbestos and wall. 

Rheostats in any case get very warm, and when working to 
capacity reach as high as 500 to 600 degrees Centigrade; when 


overloaded the coils or grids may even become red hot, therefore 
they MUST be thoroughly protected, not only from direct contact 
with, but from close proximity to anything inflammable. 

It is exceedingly difficult to give advice as to the best 
location for rheostats. Much depends on local conditions, 
and whether or not the operator wishes to vary his amperage 
while running the pictures. If he does not wish to do this 

I would strongly advise that the rheostats be located out- 
side the operating room, this by reason of the fact that 
they are in effect an electrical stove, and in summer the 
operating room is plenty hot enough without unnecessary 
heating apparatus. Then, too, when located in the operating 
room there is always the danger of film coming into acci- 
dental contact with them, with resultant call for the fire 

If in the operating room they should be located on a shelf 
near the ceiling, and as close as possible to the vent flue. 
If they cannot be located near the vent flue, then over them 
should be a metal hood connecting with a metal pipe 
(ordinary stove pipe with riveted joints will do) which should 
extend through to the open air, or, better still, connect with 
a chimney flue, the idea being to cause the large amount of 
heat generated by the rheostat to be carried off into the 
open air. 

If the operator has adjustable rheostats and desires to vary 
his amperage frequently it is quite possible to locate them 
at any desired point inside the operating room and by the 
use of levers control the dial switch from operating position 
at the projector. 

Fan Blowing on Rheostat. In one instance, at least, I 
know of an operator locating his 45 ampere rheostat in 
front of a window, with a 12 inch fan something like 2 feet 
from its side, the rheostat casing being removed. This 
rheostat supplied 45 amperes constantly to two projectors 

II hours a day. You could lay your hands on the grids at 
any time. It looked like a very good scheme. 

Examining Wire Connections. It is absolutely essential 
that the wire connections to the rheostat be frequently and 
carefully examined. Copper oxidizes under the action of 
heat, and if left too long a thin scale of oxidized metal is 
likely to form on the wire, the lug, or both. This scale will 
be very thin, and practically invisible, but nevertheless it 
has very high resistance. My advice is to take your rheostat 
contacts loose once every week and clean them thoroughly 


with emery cloth, or by scraping, particularly if the rheo- 
stats are working at or near their capacity. 

If your rheostat is delivering too much current when all 
the resistance is in, or if it gets too hot, you may reduce the 
current to any desired amount by mounting extra rheostat 
coils or coils made of No. 8 soft iron wire on porcelain in- 
sulators, as at A, Fig. 144, Page 327. Ordinary porcelain 
or "knob" insulators will do, but behind the coils must be 
placed a thickness of 54 i ncn sheet asbestos, or millboard, 
with a 1-inch air space between it and the wall, and over 
them you should place a wire screen, having about a 54 mcn 
mesh to protect them from accidental contact from film 
or other inflammable substance. 

Iron Wire Rheostats. It is quite possible to construct a 
rheostat from ordinary iron wire, but such wire has a very 
high temperature coefficient, which means that its resistance 
increases rapidly with the increase of temperature. The 
result of this is that if you build an iron-wire rheostat to 
give you the amperage you want after it has become hot, it 
will give altogether too much when you first strike the arc. 

Amount of Heat Permissible. The heat in rheostat coils 
or grids should in no circumstances exceed 900 degrees 
Fahrenheit. This temperature will make rheostat coils visible 
in a dark room, a dull red heat being approximately 1300 
Fahrenheit and a cherry red 1500. As a matter of fact this is 
too high a temperature for true economy. Five hundred de- 
grees Fahrenheit is probaply, all things considered, as high 
as your rheostat ought to reach in temperature. This would 
mean that the casing containing the coils would probably not 
reach a temperature in excess of 200 degrees Fahrenheit, 
which would eliminate all danger of fire. The life of your 
rheostat will be greatly prolonged if it does not exceed 500 
degrees Fahrenheit, and will be correspondingly shortened 
if it does exceed that temperature. You may reduce the 
temperature of your rheostats by increasing their resistance 
(thus reducing the amperage) as per Fig. 144, adding another 
rheostat in multiple to bring the amperage up to what it was. 
As a matter of fact if managers would install two rheostats 
working at half capacity, instead of one at full capacity, the 
general results would be better and the< rheostats last almost 

Two forms of resistance are employed in rheostats, viz., 
wire coils and cast-iron grids. The cast-iron grid is, how- 
ever, in effect, nothing more or less than a wire made of 



cast iron, and everything said of one applies to the other. 
A grid rheostat has certain advantages, also certain disad- 
vantages, as set below. 


(a) More difficult to replace 

broken grids than colls. 
Ob) Heavier than coll rheostat. 
Oc) Grids can be broken by heavy 

Od) Temperature co-efficient less 

fixed, therefore, somewhat 

less reliable. 


(a) Better able to withstand over- 

load and high temperatures 
without damage. 

(b) Grids less likely to sag and 

become grounded to the 
casing than colls. 

(c) Grids give longer service than 

coils and deteriorate very 

Series and Multiple Connections. Many of the younger 
operators are vastly puzzled by that really simple proposi- 
tion, "series," and "multiple" connection as applied to 

Figure 145. 

The series connection is very clearly illustrated in Fig. 
145, in which the voltage is opposed by the resistance con- 
tained in the two two-ohm rheostats, plus the resistance 
of the arc itself, the whole acting as one unit, making a total 
of four ohms plus the resistance of the arc, which latter 
wo.uld be its voltage divided by the number of amperes 
flowing. This constitutes a "series" connection. The term 
series, as applied in this connection, meaning one after the 
other, or, in practice, the connecting of two rheostats in 
such manner that their total resistance will be opposed, 
as one unit, to the voltage. 

At B, Fig. 142, we see another example of series con- 
nection, in that resistance (rheostat) C is placed in series 
with the resistance of the arc, so that the resistance of both 
act as a unit. When we connect a rheostat into a projection 
circuit we term it placing resistance "in series with the 
arc," meaning that the voltage will meet 'the opposition of 
the combined resistance of both the rheostat and the arc. 

The multiple connection is equally simple, though to the 
novice extremely puzzling. 



In Fig. 146 we see a water main, A, carrying water, say 
at 110 pounds pressure. Below is pipe B, which supplies a 
large water motor, the same being connected to A by pipes. 

Figure 146. 

controlled by stop-cocks C and D. Now it will readily be 
seen that with valve C opened and valve D closed only the 
capacity of the pipe 'controlled by valve C will reach pipe 
B and the motor, whereas, if both valves C and D are open 
the capacity of both pipes will enter pipe B. 

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Figure 147. 

Now, turning to Fig. 147, exactly the same proposition 
applies electrically; at B the upper wire, connecting to 
binding posts 1 and 3, represents water pipe A, Fig. 146, the 


lower wire, connecting to binding posts 2 and 4, and the arc 
lamp represents pipe B, the arc itself represents the water 
motor, and the resistance in each rheostat represents a pipe 
and valve corresponding to C and D, Fig. 146. The action 
of the water in Fig. 146 and the action of current in Fig. 
147 would be identical. Each rheostat is a 25 ampere, 110 
volt instrument, meaning that it has just enough resistance 
to .allow 25 amperes to flow when connected in series with a 
48 volt arc, and opposed to 110 volts pressure. Under the 
conditions shown in Fig. 147, 25 amperes will flow from the 
upper wire through binding post 1 and the resistance of the 
rheostat to binding post 2, and thence to the arc; 25 amperes 
will also flow from binding post 3 through the resistance of 
the second rheostat to binding post 4, and thence to the arc, 
joining the 25 amperes coming from the first rheostat, and 
thus 50 amperes will be delivered at the arc. 

The idea is perhaps a little more clearly shown at A, 
Fig. 147, in which the dotted line is used to represent the 
passage of the current through the resistance of the rheostat 
from binding post 1 and 2 and 3 and 4. A and B, Fig. 147, 
are identical, except that B is a, diagrammatic top view, 
whereas A is a side view showing the wires about as they 
would appear in practice. The multiple connection is shown 
photographically in Fig. 148, Page 335. 

Any number of rheostats of different voltage may be con- 
nected in series, provided the total resistance of the whole be 
sufficient to reduce the current flow to a point where the 
resistance will not be overloaded. 

Any number of rheostats, each having sufficient resis- 
tance to oppose the line voltage without overload, may be 
connected in multiple, regardless of their amperage capacity. 
For instance, a 25 ampere, a 12 ampere and a 50 ampere 110 
volt rheostat could be connected in multiple on 110 volts, 
and the result would be current delivery equal to their 
combined capacity, or 87 amperes. 

You can use a 220 volt rheostat on 110 volts, or, for that 
matter, on 60 volts, but you would only get amperes equal 
to 220 minus the arc voltage divided by the resistance of 
the rheostat. The resistance of such a rheostat would be 
(220 48) -^by its rated amperage on 220 volts. You cannot, 
however, connect 110 volt rheostats, either singly or in 
multiple, on 220 volts, since there is not resistance sufficient 
to withstand that pressure. The coils would quickly become 
overheated and would soon burn out. You may, however, 


connect two 110 volt rheostats in series on 220 volt current 
(though they would be slightly overloaded), by reason of 
the fact that you would be, in effect, making one rheostat out 
of the two, and would thus present double the resistance 
required for 110 volts. 

You may use a rheostat built for certain voltage on that 
pressure, or anything less than that pressure, but you cannot 
use a rheostat on a higher pressure than it was intended for, 
except it be placed in series with additional resistance. 

This, however, may be qualified to the extent that a 
rheostat built for a certain voltage may usually be used 
on current five, ten, or even fifteen volts in excess of that 

A. C. and D. C. Rheostats. There is no such thing as 
a "D. C." or an "A. C." rheostat. Any rheostat will work on 
either A. C. or D. C., but a rheostat that will deliver 30 amperes 
when working with a D. C. projection arc, on, say, 110 volts 
pressure, will deliver considerably more on the same voltage 
A. C., by reason of the fact that the A. C. projection arc is 
shorter, hence offers less resistance, so that the total resis- 
tance opposed to the current is reduced. 

This, however, is again qualified by the fact that there is a 
tendency to induction when a wire-coil rheostat is used on 
A. C., which has the effect of adding inductive resistance, 
or, in other words, magnetic kick. The amount of inductive 
resistance thus set up will vary with the size of the coils, 
their length and the closeness of the spirals. It amounts to 
something, but not very much. The inductive effect, however, 
causes vibration in the coils, and as a result some wire-coil 
rheostats are very noisy when used on A. C. This noise may 
be reduced by packing the center of the wire coils tightly 
with shredded asbestos forced in at the end of each coil. 

The use of rheostats on A. C. is very, very bad practice. It 
is unnecessarily wasteful. Where alternating current is used 
rheostats should be replaced by low voltage transformers. See 
Page 343, or, better still, with a mercury arc rectifier or motor 
generator set, see index. 

If, however, for any reason it is necessary to use resistance 
in A. C. projection circuits I would advise the grid type, 
since they are likely to be a great deal less noisy; also there 
is much less inductive effect; therefore the resistance will 
be found to be more stable. 

Rheostats Extremely Wasteful. The real use of the 
rheostat in the projection circuit is to consume the differ- 


ence between the line voltage and the arc voltage, or, in 
other words, to break the line voltage down to the value 
of the arc voltage. This represents an absolute waste of 
energy, since the difference between the line voltage and 
the arc voltage is, and must be, dissipated in the form of 
utterly useless heat generated by the rheostat, and this wast- 
ed energy is all registered on the meter and must be paid for 
by the theatre. 

Suppose, for example, the current supply be 110 volts, 
and that we use 40 amperes at the arc. Voltage times 
amperes equals watts, therefore 110X40 = 4400 watts reg- 
istered by the meter. The average voltage of a D. C. pro- 
jection arc is only 48, therefore there must be consumed in 
the rheostat 110 48 = 62 volts, which will be registered 
on the meter as 62 X 40 = 2480 watts, this amount being 
absolute waste. We are using a total of 4400 watts, and 
only actually employing 4400 2480 = 1920 watts in the 
production of light. At this voltage and amperage the rheo- 
stat is 43J4 per cent, efficient. 

This is bad enough, but if the voltage be higher, say 220, 
then ,the proportion of waste becomes literally enormous. 
Using 40 amperes from 220 volt lines through a rheostat 
would mean 220 X 40 = 8800 watts registered by the meter, 
whereas the actual wattage at the arc is, as in the former case, 
48 X 40 = 1920 watts, so there is wasted in the resistance of 
the rheostat 8800 1920 = 6880 watts, or about 3 l / 2 times 
as much energy as is actually employed in the production of 
light. On the other hand, if the voltage were only 60 or 70 
then the waste in resistance would be correspondingly less, 
and it is for this reason why the author has always advised 
theatre managers when purchasing a light plant for their 
theatre to get a 60 or 70 volt generator. 

From what has been said the idea may be gained that if 
direct current were generated at from 45 to 55 volts, or 
alternating current at 30 to 35 volts, it would be possible 
to operate without any resistance at all, thus eliminating all 
waste. This, however, is only true where generators of a 
certain type, built especially for this kind of work, are used. 
By the use of certain types of generators which in themselves 
automatically regulate the voltage, hence the current flow, 
it is possible to operate a projection arc without any resis- 
tance at all (See Motor Generator Sets, further on), but 
this cannot be done when using the usual type of generator. 
Resistance performs two functions, vfiz., regulates the am- 



perage by regulating the voltage and supplies a steadying 
influence, or sort of "cushion" for the arc. Without this 
steadying influence, or its equivalent in another form, such 
as a generator of the type mentioned, the arc would be so 
unstable that it could not be handled at all; also it would 
not. be practical to strike the arc in the first place, because 
when the carbons were brought together it would establish 
a dead, short circuit which would instantly blow the fuses. 
Note. I have said that all pressure above arc voltage 
represents waste, but this is not strictly true as applied to 
projection arcs taking current through rheostats. Under 
these conditions if the suply be below 60 volts the necessary 
resistance is not sufficient to steady the arc, therefore, strict- 
ly speaking, while the voltage between a 60 volt supply 
pressure and arc voltage represents waste, still it is necessary 
waste, whereas when the supply voltage is more than 60 all 
over that figure is unnecessary waste. 


Figure 148. 

Note b. It may be remarked that traveling exhibitors 
have installed a small generator in an automobile and, using 
the auto engine for power, have operated a projection lamp 
without resistance in circuit. This is possible with a small 
generator working right up to capacity, but is not possible 
when taking current from power lines or a generator of 
considerable capacity. 

Figuring Rheostat Connections. In Fig. 148 we see an 
Edison adjustable, grid rheostat, with part of the casing re- 
moved to show the grid bank, connected in multiple with a 
Power's non-adjustable coil rheostat, both 110 volt instru- 


The Power's is a 25 ampere, 110 volt, and the Edison a 25 
to 40 ampere, 110 volt rheostat. We will therefore get 25 
amperes through one, and from 25 to 40 through the other, 
according to how the adjustment switch is turned. We will 
have a total current of from 25 + 25 = 50, to 25 + 40 = 65 am- 
peres at the arc, with this combination. With the same two 
connected in series on D. C. we would get from 10 to 12+ 
amperes. It is figured as follows: The Power's is a 25 am- 
pere, 110 volt instrument, therefore, has (110 48) -f- 25 = 
2y 2 ohms resistance. The Edison, when working at 25 amperes 
must have the same resistance, hence there will be a total 
of 2*/2. + 2y 2 ohms when they are opposed to the voltage in 
series. The resistance of the arc will be approximately 1 
ohm, hence (110 48)^-2^+2^ + 1 will equal the amper- 
age when the Edison is on the 25 ampere contact. This is 
practically 10 amperes. If the Edison is set on the 40 am- 
pere contact we would then have (110 48)^-40 equal prac- 
tically \ l / 2 ohms, which added to the resistance of the Pow- 
er's makes (2 l / 2 + \ l / 2 } 4 ohms. We would, therefore, have 
(110 48) -f- 2y 2 + 1J*X1 = 12+ amperes delivery. If the 
current be A. C., then we would have (110 35) -f- 5 = 15 
amperes (not taking the inductive resistance into account); 
the A. C. arc voltage being 35, instead of 48 as in D. C. 

Let it be clearly understood, however, that these figures are 
only approximate. It is impossible to be accurate for the rea- 
son that arc resistance varies with the length of the arc; 
also the rheostatic resistance varies with (a) temperature 
of the coils or grids; (b) with their age. Also, merely 
because a rheostat is stamped' "110 volt, 25 ampere," it does 
not follow it has exactly the resistance this would indicate. 
Moreover, the supply voltage may not be just what you 
think it is. 

As a matter of fact, a wire-coil rheostat rated at 25 am- 
peres, and which delivers that amperage when new, will not 
do so after it has been used for a time. The resistance of 
wire coils rises gradually for a time, and then remains prac- 
tically stationary until the coils finally give out entirely. 
When the resistance reaches its highest point it will usually 
be found that the "25 ampere" wire coil rheostat is really 
delivering about 20 amperes. After using a wire coil rheostat 
for a month or more you will be more nearly correct if you 
subtract five amperes from every 25 amperes of its rated 


This may or may not apply to any considerable extent to 
cast iron grids. It is claimed that the resistance of cast iron 
remains constant, or practically so, but of this I am not 

Resistance Devices 

EACH machine manufacturer puts out a rheostat, and 
some of them put out two or three different kinds. 
The Nicholas Power Company,- for instance, puts out a 
grid rheostat and two or three different varieties of wire 
coil rheostats. I do not believe it is necessary to present 
illustrations of all these different devices, particularly in view 
of the fact that they all operate on precisely the same prin- 
ciple, and in exactly the same way. Wire coil rheostats are 
nothing more or less than a long piece of resistance wire 
coiled up into spirals in order to save space, the coils being 
mounted on an iron frame, from which they are thoroughly 
insulated, the whole being protected by a sheet metal guard 
or cover. The current enters at one binding post, flows 
through the resistance, and leaves at the other binding 'post. 
The rheostat is connected into either wire of the circuit, 
though most operators prefer the positive wire. 

Figure 149. 

Fig. 149 shows an ordinary rheostat "coil." In mounting 
this coil must be stretched just a little enough so that the 
spirals will be at least 1/16 of an inch apart. This is im- 
portant, by reason of the fact that if the spirals touch each 
other, then the current will simply jump through the coil, 
instead of flowing through the entire length of the wire. 
The effect of the spirals touching would tend to eliminate 
a large percentage of the resistance. 

Fig. 150 illustrates one grid of a rheostat. It will be ob- 
served that it is, in effect, precisely the same as the wire 
coil illustrated in Fig. 149. To all intents and purposes it 
is a long wire made of cast iron coiled up to save space. 



In Fig. 151 we see a photographic representation of an 
adjustable grid rheostat. Thirteen to 26, inclusive, are cast 

Figure 150. 

iron grids, the same as the one illustrated in Fig. 143. The 
edges of these grids are protected from breakage by metal 

Figure 151. 

guards, 1 and 3, Fig. 151, inside of which is a layer of 
asbestos insulation. At the top, X is a metal spacing 


washer; next to it, represents a similar spacing washer, but 
between it and the grids are insulating washers. Next comes 
another current carrying washer, and then another insulat- 
ing washer, the whole being mounted on tie-rods 4-4. Now 
between grids 25 and 26 at the bottom end is an insulated 
spacing washer, and next to it, F is a current carrying 
washer, and so on. The grids are insulated from the tie- 
rods, therefore you will readily see that current entering 
at binding post 9 will pass through the connections to binding 
post G, thence to grid 26, up its length, across current carry- 
ing washer X, down grid 25, across current carrying washer 
F, up grid 24, and so on until it reaches an outlet. At the 
other end, 11 is a binding post to which the wire is attached, 
this post connecting to central switch post 6 through a 
wire, 12, represented by dotted line; 1, 2, 3, 4 and 5 are con- 
tact buttons connected to the grids at points A, B, C, D 
and E. 

The lever is now on contact 5, so that current entering 
at binding post 9 will flow to binding post G and through 
the grids until it reaches binding post E, whence it will flow 
up through the wire jumper to switch contact 5, across the 
switch lever to post 6, down wire 12 to binding post 11, and 
thence to the lamp. This, you will readily see, " cuts out " 
grids 13, 14, 15, 16, 17, 18, 19 and 20. If we swing switch 
lever 7 over to contact button 1 the current must then travel 
through the grids until it reaches binding post A, whence 
it will flow to contact 1 and around through the switch lever 
and wire 12 to binding post 11, thence to the lamp. There- 
fore, with switch lever 7 on contact 1 you will be getting all 
the resistance that particular rheostat is capable of supply- 
ing, and will be reducing the voltage, and therefore the am- 
perage as much as that rheostat will reduce it. 

Binding post 8 is an auxiliary binding post not found on 
most rheostats. It is for the purpose of allowing the rheo- 
stat to be used on low voltage current. 

With switch lever 7 on contact 5, and the wire connected 
to binding posts 11 and 9, you still have the resistance sup- 
plied by grids 21, 22, 23, 24, 25 and 26. This is what is 
known as the "fixed resistance" of the rheostat. If you 
desire to use the rheostat on current of very low voltage 
this resistance might be too much to supply the required 
amperage, and by changing the connection from binding 
post 9 to binding post 8 you will cut out coils 25 and 26, 
thus lowering the fixed resistance by one-third, and increas- 
ing the amperage accordingly. 



This is made somewhat more plain in Fig. 152, in which 
the same numbers are used. By closely examining Fig. 152, 
you will observe the mica insulating washers, which are 
shown at 10 in both figures, you will see they are only used 
in alternate spaces. The Power Company puts this type of 
rheostat out for both 110 and 220 volt current. The weight 
of the 220 volt rheostat is practically double that of the 
110 volt instrument. 

Figure 152. 

In connecting a rheostat, wires are run from the main 
operating room cutout to one side of the machine table 
switch, and one of the contacts at the other end of the 
machine table switch is connected, using asbestos covered 
stranded wire, direct to one of the binding posts of the 
lamp. From the other machine switch binding post we run 
an asbestos strand covered wire to one (either) of the 
rheostat binding posts, and from the other rheostat binding 
post we run another asbestos covered strand wire to the 
other binding post of the lamp. Most operators prefer the 
resistance in the positive wire when using D. C., but it 
really does not make any particular difference which wine 
it is in. 

The rheostat shown in Fig. 151 may be disassembled by 
removing its cover, and loosening nuts 4-4 which hold the 
grid bank together. Having removed these nuts the grids 
can be slipped off the tie-rods. In reassembling be very sure 


you get the insulating and current carrying washers X and O in 
their proper relation. If you don't you will have trouble. Also 
when the reassembling is complete be sure to set up tie-rods 4-4 
good and tight. 

Caution. Be sure that lever 7 makes firm contact with 
the contact buttons, since otherwise there will be arcing and 
heating. Should these contacts become roughened after a 
time, carefully dress them up with No. 00 emery cloth or 
paper, at the same time smoothing up the contact face of 
the lever. Wrapping the emery around a small file will 
enable you to do a better job. All adjustable rheostats have 
the same connections as the one shown in Fig. 151, except 
that few have auxiliary binding post 8. The 220 volt grid 
rheostat is connected into the circuit just the same as is the 
110 volt one. 

Some rheostats are adjustable, and some are non-adjust- 
able, the latter usually having two binding posts to which 
wires are connected. They offer fixed resistance which can- 
not be changed. This kind of resistance is not the best, 
however, for several reasons, one of which lies in the fact 

Figure 153. 

that a new rheostat has considerable less resistance than it 
has after it has been in use for a time. Therefore, if for no 
other reason it is desirable that one be able to cut out some 
of the coils when the resistance becomes greater through use. 
As between the grid and wire coil rheostat I would advise 
the wire coil for road use, by reason of its comparatively 
light weight, and the grid rheostat for theatrical use, be- 
cause it is rugged in its construction, deteriorates much less 
rapidly and, therefore, lasts longer. For road use the 
Nicholas Power Company puts out a wire coil rheostat 
made in round form, illustrated in Fig. 153. 



My reason for recommending this rheostat is it is light in 
weight and very flexible in its electrical action. 

In Fig. 154 the top of this rheostat is shown at A, on the 
left. Connections are made to binding post B-B, and all 
the coils from 1 to 14 are thus placed in series with each 
other, but since binding post B connects to the central 
switch post by means of a copper jumper the current will 
only pass through the number of coils necessary to reach 
the lever. Therefore, if the lever is on contact 4 the re- 
sistance of coils 1, 2 and 3 would be eliminated. At B, on 

Figure 154. 

the right, this rheostat is shown with its two sides in mul- 
tiple. It is the same as though you connected two rheostats, 
each one having the resistance supplied by half the total 
number of coils in the rheostat, in multiple. The current 
enters at binding posts B-B, flows through the coils on the 
left to 8 and through the coils on the right to 7, and thence 
to the lamp. You thus get the full capacity of these two 
banks of coils, but this can only be used on 110 or less voltage, 
whereas the connection at A can be used on current up to 
240 volts. When using connection B, Fig. 154, the lever must 
be set on contact 1. Possibly you can increase the current 
somewhat by moving it to contact 2 or 3, but beyond that 
the remaining coils on that side will most likely get red hot. 



The Transformer 

THE transformer .is a device for changing alternating 
current of a given cycle (frequency) and voltage to 
the alternating current of the same cycle but of a 
different voltage and amperage. In general, the volts times 
amperes taken from the supply line is equal to the volts 
times amperes (volt amperes) given off at the secondary, 
less the loss in the transformer itself, which loss varies from 
10 to 20 per cent. 

The standard transformer is made up with two separate 
coils which are insulated from each other, one coil being 
called "primary " and the other coil being called " sec- 
ondary." There are modifications of transformers which are 
designed as " auto transformers," in which the transform- 
ing action is obtained more efficiently than with a straight 
transformer, but in which the windings are not insulated 
from one another, the secondary winding becoming a part of 
the primai y winding. To 
this class belong most 
transformers used in the 
operating rooms for con- 
trolling the projection arc. 
Another modification is a 
reactance coil, or choke coil, 
as it is sometimes called. 
In this device the choking 
effect of the transformer Figure 155. 

is obtained, but the am- 
peres taken from the secondary side will always be the same as 
on the primary side, although the volts on the secondary side 
will differ from the volts on the primary side. This device is 
less efficient than either the transformer or auto transformer. 

A transformer (or auto transformer) may either increase 
the voltage and decrease the amperage, in which case it is 
called a step-up transformer, or it may decrease the voltage 
and increase the amperage, in which case it is called a step- 
down transformer. 

Fig. 155 represents the diagrammatic connections of a 
straight transformer. It will be noted that the windings 



are independent of one another, although they both sur- 
round portions of the same core or magnetic circuit. 

Fig. 156 represents the diagrammatic arrangement of an 
auto transformer. It will be noted that with the two wind- 
ings connected together so as to form practically one coil, 
due to the fact that the current in the primary is transformed 
through only a part of the winding, the losses become less 
tlhan the losses in the transformer represented in Fig. 155. 
This results in a smaller and more efficient construction 
than in the straight transformer. 

Fig. 159 is a diagrammatic connection of a reactance or 
choke coil. With this arrangement no saving in wire size 
is possible, because the same amount of current (amperes) 

consumed in the arc must be 
taken from the line. 

In a transformer or auto 
transformer the amount of 
current in secondary depends 
on the ratio of turns (number 
of turns primary divided by 
number of turns secondary). 
If the primary winding were 
made up with 20 turns and 
the secondary winding made 
up with 10 turns, this would 
be a ratio of 2 to 1, and each 
two amperes in the secondary 
would require one ampere 
from the primary. The volts 
on the secondary, however, 
would be only one-half of the 
volts on the primary. 

Referring to Fig. 157, A and 
B are the wires of the sup- 
ply circuit; C and D are wires leading to the primary coil 
from the main supply wires; I and J are wires leading from 
the secondary coil to arc lamp K; L is the laminated iron 

The primary and secondary coils may be wound one over 
the other and inserted in the opening in the core, or they 
may be wound as shown, or in other ways, the method in 
Fig. 155 being merely selected to show the idea. The wires 
of the coils are themselves covered with a special form of 
insulation. The coils are insulated from the iron core. 

Figure 156. 



Neither coil has any mechanical or electrial connection of 
any kind whatsoever with the other coils or the core. 

The core itself is built up of thin sheets of annealed 
steel. It is essential that these sheets be very thin, the exact 
thickness depending on the frequency of the current. Each 
s(heet is painted on both sides with an insulating compound, 
or other methods to insulate are used, after which the s'heets 
are clamped firmly together and the primary and secondary 
coils are wound on the core thus formed, over a layer of 
insulating material, and the two coils and the core form the 

The action is as follows: When the switch on the pri- 
mary side is closed the current which flows through the 
primary coil magnetizes 
the iron core and sets up a 
powerful magnetic field, 
Which has the effect of mak- 
ing a choke coil out of the 
primary coil, and a choke 
coil so powerful that prac- 
tically no current at all will 
flow when the secondary 
circuit is open. The mag- 
netic field thus created sur- 
rounds both primary and 
secondary coils, so that 
w.hile these coils have ab- 
solutely no mechanical con- 
nection with each other or 
with the core, and are, in 
fact, thoroughly insulated 
from the core, they do have 
a magnetic connection, which 
acts as follows : 

It is one of the laws of Figure 157. 

electrdcity that) all, wires carry- 
ing alternating current are surrounded with what is known as a 
"magnetic field"; that is to say, for a certain distance sur- 
rounding a wire carrying A. C. the air is permeated with 
magnetism. Now if another wire be placed within this mag- 
netic field, as per Fig. 158, although there be no mechanical 
connection of any kind between the two wires, if wire A 
carries A. C. then there will be an induced electro-motive 
force set up in wire B, though under the conditions set forth 
the effect would be too slight to be perceptible except to a 



Figure 158. 

very delicate galvanometer. Fig. 158 merely illustrates the 
theory upon which the transformer depends for its action. 
In transformers instead of wire A we have a great many 
wires in the primary coil or rather one wire passing through 
the magnetic field a great many times, and instead of wire 

B a great many wires in the 
secondary coil, or one wire 
passing through the magnetic 
field a great many times. We 
also have an iron core which 
enormously intensifies the mag- 
netic field, and thus the feeble 
action in wire B, Fig. 158, be- 
comes enormously powerful, and' 
we have the "transformer." 

The action of the transformer 
is entirely automatic, and it 
depends entirely for its action 
on magnetic inductance. The 
secondary current in flowing 
through the secondary coil magnetizes the core, but in the 
opposite direction to the primary, therefore when current 
flows in the secondary the primary current increases just 
enough so that combined effect of the two windings remains 

the same. It therefore fol- 

lows that when the load of 
a transformer is increased 
the primary winding auto- 
matically takes additional 
current from the supply 
wires just sufficient to sup- 
ply the added load on the 
secondary, therefore the 
automatic action of the 
transformer depends on the 
balanced magnetizing action 
of the primary and second- 
ary circuits. 

Referring to Fig. 156, A 
and B are the supply lines, 
C and D are the wires 

Figure 159. 

feeding the auto transformer, E the winding, including both 
primary and secondary, F and G the wires feeding the arc K, 
and L is the iron core. 

It is to be noted the entire coil E is connected across the 



supply lines and that a tap T is brought out so that the 
section of E from S to T forms the secondary while the 
whole coil forms the primary. The action electrically and 
magnetically is the same as in a standard transformer. 

The choke coil, also called a "reactance" coil, Fig. 159, 
represents what might be called magnetic resistance. If an 
iron core consisting, in practice, of thin sheets of metal, be 
built up, and one of the in- 
sulated wires of an alternating 
circuit be wrapped a number 
of times around it, as shown, 
there will be a magnetic kick 
or reactance set up, which 
will have the effect of offer- 
ing resistance to current flow. 
This is called "magnetic kick," 
or "reactance." The practical 
effect upon current flow is 
essentially the same as that 
of the rheostat. The mag- 
netic field set up around the 
core of the coil has the effect 
of creating a counter E. M. F., 
which opposes the line voltage 
and reduces it. The choke 
coil is, however, very much 
more economical in operation 
than is the rheostat, but is not 
nearly so satisfactory for the 
production of projection light 
as is the transformer or auto 
transformer, largely by reason 
of the fact that it has a ten- 
dency to produce flaming at 
the carbons, and where it is 
used difficulty is found in con- 
centrating the crater into a 
small area. The transformer 
has, of course, a power factor, 
but I hardly think any good purpose will be served by going 
into that matter, particularly in view of the fact that the 
author can no longer recommend the use of operating room 
transformers. True these instruments are quite efficient and 
by their use a very good illumination may be had. Still, 
the use of alternating current at the projection arc is out of 


Figure 160. 


date, and ought to be entirely discontinued. Motor-gen- 
erator sets and mercury arc rectifiers have been brought to 
a high state of perfection, so there is now no good reason 
why alternating current should be used for projection pur- 
poses, nor is its use efficient, when viewed from the stand- 
point of curtain brilliancy. By this I mean that, whereas it 
is possible to secure practically as excellent an illumination 
with alternating current as with direct current, still it will 
take practically double the amperage to do it. In fact, for 
a picture of given size a better screen result will be had 
with 25 amperes D. C. than with 50 amperes A. C., and 
in order to get the same result in illumination as that pro- 
duced by 40 amperes D. C. it would be necessary to use 
fully 80 amperes A. C. Therefore, even allowing that the 
transformer has a higher efficiency than the rectifier or 
motor-generator set, still if equal screen illumination is had 
it will cost more to use A. C. 

Where the coils are wound around opposite legs of the 
core, as in Fig. 155, the transformer is called a "core" 
transformer; where the coil is wound around the central leg 
of the core (inside the outer legs of the core) it is known 
as the "shell" type, Fig. 157. 

Please let it be understood that I am not entering into all 
the details of transformer construction. The details of con- 
struction have much to do with the efficient performance of 
a transformer, but all I seek to accomplish in this article is 
to give the operator a fairly comprehensive understanding of 
the theory upon which the transformer works not to give 
him instructions enabling him to build one. That calls 
for very careful calculations and experiment, which can only 
be made by a duly qualified electrical engineer. 

Transformers may be built to deliver current to a three- 
wire secondary from which two voltages may be had; for in- 
stance, 220 and 110. This is illustrated in Fig. 160. As a 
matter of fact usually alternating current three-wire systems 
are two-wire circuits up to the transformer, and beyond the 
transformer become three-wire systems merely by either the 
peculiarity of construction of the transformer or the method 
of hitching up two transformers. 

The operator is as a general proposition only interested 
in the theory of the transformer and the practical operation 
of the low voltage transformer commonly called "compens- 
arc," "economizer," "inductor," which ordinarily takes 110 



or 220 volts supply from the line and delivers secondary cur- 
rent at arc voltage, and this is the type of transformer to 
which we will devote our attention. 

As has already been remarked, volts times amperes taken 
from the line equals volts times amperes delivered on the 
secondary, less the loss in the transformer which, as I have 
already remarked, may run anywhere from 10 to 20 per cent. 

In operating a projection arc lamp it is necessary at times 
to vary the amperes. Now the secondary of a transformer 
works against a slight resistance of the secondary circuit 
wires and a considerable re- 
sistance of the projection 
arc, therefore the current 
flow against this particular 
fixed resistance can either 
be increased or decreased 
by increasing or decreasing 
the voltage of the second- 

As has already been re- 
marked, the voltage of the 
secondary will depend upon 
the relative number of 
turns in the primary and 
the secondary coil. The 
greater the number of turns 
in the primary with relation 
to the number of turns in 
the secondary the less the 
voltage of the secondary. 

It is a known fact that 
the best voltage across an 
alternating current arc is 
approximately 35 volts. In 
order to keep the arc burn- 
ing steadily it is always 

necessary to have a steadying resistance or a reactance in the 
arc circuit. One advantage of reactance for steadying the arc 
is that there is very little power lost in the reactance, whereas 
with resistance all of the steadying effect is turned into heat, 
and, therefore, means a lot of lost power. Reactance can be 
obtained only on alternating circuits. 

In order to change the current at the arc it is necessary, 
therefore, to change the steadying reactance when using a 


Figure 161. 



transformer or auto transformer. This is done in different 
ways. In some cases the turns in the primary are changed, 
and in this way the reactance, or magnetic choking, is 
changed so as to change the value of current at the arc. 

This fact is taken advantage of as per Fig. 161, in which 
A, B, C are buttons and D ,a lever which completes the cir- 
cuit of the primary coil through one of these buttons. It 
will readily be seen that if lever D be on button A the num- 
ber of turns in the primary will be decreased, and, since the 
turns in the secondary remain fixed, the voltage of the sec- 
ondary and consequently its amperage will be raised. By 
moving lever D to button B or C the number of turns in 
the primary is increased, and, therefore, the voltage and 
amperage in the secondary is decreased. 

Another scheme, used in the Fort Wayne A. C. compensarc, 
is to have small additional reactance coils, which are cut in 
or cut out of circuit by means of a switch. These are 
placed in the secondary circuit, so that the secondary voltage 

Figure 162. 

remains the same for the different values of current, and this 
gives the same length of arc and condition of the crater on 
the different steps. See Fig. 162. 



Fusing Projection Circuits Where Transformer is Used. 
Let it be clearly understood that the term "transformer," 
as here used, means the low-voltage transformer commonly 
termed "Economizer," "Inductor," "Compensarc," etc. Be- 
fore reading this, however, I would recommend the oper- 
ator to turn to Page 343, and study the electrical action of 
these devices. 

When dealing with transformers it must be clearly under- 
stood that one ampere from a 110 volt line becomes con- 
siderably more than two amperes at the 35 volt projection 
arc, and that one ampere from a 220 volt line becomes ap- 
proximately between five and six amperes at the 35 volt arc. 
Let it also be clearly understood that, for the purpose of 
calculating, we assume the voltage of the A. C. projection 
arc, and therefore the voltage of the secondary of the trans- 
former, to be 35, although it may range anywhere between 
30 and 40. 

This brings about a peculiar and ap- 
parently very little understood condition 
as applied to fusing. Almost all trans- 
formers (remember I am speaking of 
economizers, etc.) are fused on their 
primary side only. This is bad practice. 

Fig. 163 is the diagrammatic representa- 
tion of a transformer-controlled projection 

Note. Error: Switch 7 should be between fuses 1-1 and transformer 3. 

Figure 163. 

circuit in which 1-1 are the fuses at the beginning of the 
primary circuit, either at the operating room distribution 
panel or the main house switchboard, as the case may be; 
2-2 are the lines from 1-1 to the transformer; 3 is the trans- 
former; 4-4 the lines from the transformer secondary to 
fuses 5, and 6-6 are the lines from secondary fuses 5 to 
machine table switch 7. All these may be rubber covered 
wire, but lines 4-4 and 6-6 must be of sufficient size to ac- 


commodate the full amperage capacity of secondary fuses. 
Line 2-2 should not be less than No. 6 B. & S., and it would 
be still better to have them No. 4, because it may become 
necessary, in case of breakdown or for some other reason, 
to remove the transformer and substitute a rheostat, in 
which case you would not want to pull less than 50 or 60 
amperes, and No. 6 R. C. is only rated at 50, No. 5 at 
55, and No. 4 at 60 amperes. 

The ordinary procedure is to install wires 2-2 just large 
enough to carry the secondary capacity of the transformer, 
but, for reasons already set forth, this is not the best prac- 
tice. If wires 4-4 and 6-6 are rubber covered, then No. 4 
must be used, since practically all transformers (econo- 
mizers, compensarcs, inductors, etc.) have a 60 ampere sec- 
ondary capacity, but if wires 4-4 and 6-6 are asbestos covered, 
they come under the weatherproof rating, and No. 6 is large 
enough, since No. 6 weatherproof is rated at 70 amperes. 
Wires 8-8, from machine table switch to lamp, must be 
asbestos covered stranded No. 6, unless a special transformer 
delivering more than a 70 ampere secondary current is 
installed, in which case they must be large enough to ac- 
commodate the current. Fuses 1-1 are merely designed to 
protect wires 2-2 and the transformer primary coil, but inas- 
much as No. 6 wire will accommodate nearly three times the 
primary current capacity of the transformer, they really, in 
effect, protect only the transformer primary coil, and for 
the ordinary economizer delivering a maximum of 60 am- 
peres at the arc, they should be 30 ampere capacity. Some 
transformers will deliver more than 60 amperes secondary, 
especially if the voltage be a little higher than rated, but 
you will -find that 30 ampere fuses will meet all requirements. 
The secondary may be fused to 65 amperes, which will give 
a 5 ampere leeway. But, however, if 65 be found insufficient, 
no harm will be done by installing others of 70 ampere 

The reason for requiring fuses on the secondary as well 
as on the primary are twofold; First, some operators and 
managers locate the transformer outside the operating room, 
even putting it down in the basement. This is very bad prac- 
tice, but nevertheless they do it, and then, exercising still 
more and greater bad judgment, stick 50 or 60 ampere fuses 
on the primary. The inspector is not likely to see it, because 
it is an out of the way place. For practical purposes they may 
just as well not fuse at all, because with 110 volt transformers, 
60 ampere primary fuses would deliver about 150 amperes on 


the secondary, whereas with a 220 volt supply it would 
give nearly 300. Second, except in small sizes, cartridge and 
plug fuses are only made in multiples of 5 amperes, that is to 
say 20, 25, 30, 35, etc. Now with a 110 volt supply 30 ampere 
fuses will deliver approximately 60 amperes on the secondary, 
but the capacity of the fuses and of the transformer is so 
nearly :alike that there might be trouble with 30 ampere 
fuses blowing. If, however, you install others of 35 ampere 
capacity, the next size, it makes a possible difference of 
between 10 and 15 amperes at the arc, with the 110 volt 
supply, and between 20 and 30 amperes with the 220 volt 
supply, whereas 5 amperes difference in the fuses on the 
secondary means 5 amperes, and no more; therefore it is 
possible to fuse much more rationally on the secondary than 
it is on the primary. 



This device is manufactured by the Fort Wayne Electric 
Works for use on alternating current circuits only. It is 
self-contained and requires no auxiliary rheostat or other 
controlling mechanism. Before in- 
stalling the compensarc examine the 
name plate to see if the rating agrees 
with the frequency and line voltage 
of your service. 

Place the compensarc directly 
beneath the lamp house of the pro-i 
jection machine if possible, other- 
wise in some position convenient 
to the operator to allow him to 
adjust the amperage of his arc. 
Connect both wires from the 
Power Company's service through 
a double-pole* fused switch to the 
two terminals of the compensarc 
marked "LINE." Connect two ter- 
minals marked "LAMP" to the projec- 
tion arc terminals through the 
double-pole operating switch on the 
projection machine. As this is an 
A. C. device there are no positive ^^^ 

or negative wires. ^^p Figure 164. 



Fig. 165 is a diagram of connections for the A. C. com- 
pensarc. The primary or line wires should be fused to about 
half the maximum current at the lamp. This would ordi- 
narily require about a 30-ampere fuse. 

Note. This diagram supplied by the manufacturer. The author 
does not agree with omitting fuses from the secondary circuit. 
See Fig. 163. 

Figure 165. 

This device is adjustable in three steps, which steps have 
been found to meet the general service conditions. 

When the switch on the compensarc is open no current 
flows through the lamp, but the operator should not handle 
his carbons without opening the operating switch on the projec- 
tion machine, because if the outside lines have a ground and the 
operating room is grounded the operator can receive a shock 
of full-line potential. When through with the show open the 
primary line switch. 

Fig. 166 shows the slate top of 
the A. C. compensarc and the 
switch blade. Throwing the switch 
blade in contact with the first clip 
of the switch (Fig. 166) gives an 
adjustment so that with the car- 
bons separated about three-six- 
teenth of an inch the current flow- 
ing through the projection lamp Figure 166. 


will be approximately 30 amperes. In contact with the sec- 
ond clip of switch the adjustment changes so that approxi- 
mately 40 amperes flow through the arc. Throwing the 
switch blade over to the third clip allows approximately 60 
amperes to flow through the lamp. The manufacturer recom- 
mends the use of five-eighths-inch cored carbon upper and 

In order to determine if your compensarc is in good con- 
dition on all three steps, first, start the arc on any one of the 
steps, then jump the switch quickly to the other two steps in 
succession, watching the light. There should be an appre- 
ciable difference in the light, which you should be able to de- 
tect in trying this several times. If you think the compens- 
arc is heating too much do not attempt to judge the tem- 
perature by your hand; use a thermometer on the hottest 
part. Lean the thermometer in contact with the hottest part 
for 5 or 10 minutes and the temperature should never exceed 
40 degrees C. or 72 degrees F. above the room temperature. 

To obtain the best results carefully observe the following: 

(1) Make sure the two leads marked "lamp" are connected 
to the projection arc lamp through operating switch on the 
projection machine. 

(2) Always open operating switch on projection machine 
when changing carbons, to eliminate possibility of shock due 
to grounds on the power system. 

(3) Connect to leads marked line directly to the power 
line through a fused double-pole switch. When through 
using the compensarc open the line switch. 

(4) Never connect any resistance in series with the com- 
pensarc either on the line or lamp side. 

(5) Be sure the line voltage and frequency agree with the 
voltage and frequency marked on compensarc nameplate. 

(6) Be sure all connections are perfectly clean and tight 
and see that adjusting switch has not been damaged in 

(7) Do not try to use any more current than is required to 
obtain a good picture. 

(8) Do not overload your carbons, as this will produce a 
very noisy arc. 

(9) Do not separate carbons too far; a three-sixteenth- 
inch separation on five-eighths cored carbons will give good 
satisfaction with 40 amperes. 



Plate 1, Figure 167. 


The Edison Company 
claims a very high effi- 
ciency and a simple ad- 
justing mechanism for 
its transformer, which is 
illustrated in Plate 1. 

Wiping Connections. 
The device has five leads 
entering. At one side, 
directly under that part 
of the top in which the 
word "Lamp" is cast, are 
the secondary wires, which 
are to be connected direct- 
ly to the arc lamp, either 
wire to either lamp bind- 
ing post. 

Plate 2, Figure 168. 



The three wires entering the opposite side are the primary 
lines. The wires directly under the word "Common" must 
always be connected to one side of the line switch. One of 
the other two wires should be connected to the other side of 
the line switch, but which one is to be so connected will de- 
pend upon the line voltage. This is all made clear in Fig. 
168, so that no mistake can possibly be made. The end of 
the wire not in use must be carefully wrapped with insu- 
lating tape and left dead. 

To Line 
Machine Switch 

Common TOO 



Fig. A 

To Line 
Machine Switch 

Common WO 


108-1 10 OR 120 VOLTS 

Fig. B 

* II 

To Line 



Common 200 220 

Fig. C 


To Line 

Common 200 220 
Fig. D 

Plate 3, Figure 169. 

For further information see the wiring diagram in Fig. 
169, which gives all necessary information with; regard to 
both the 110 volt and 220 volt transformer connections. 

Range of Adjustments. In Plates 1 and 2 you see a handle 
or crank on top of the transformer. This handle operates 
adjusting plugs which vary with the current at the arc. Cast 
into the cover on top of the transformer case, Plate 2, are 



two arrows, marked respectively "Raise" and "Lower." 
Turning toward "Raise" you will raise the voltage, and 
hence the amperage at the arc; the opposite direction lowers 
the voltage, hence the amperage at the arc. The crank or 
handle raises or lowers leakage plugs in the magnetic cir- 
cuit, the same being placed between the primary and second- 
ary windings, thus increasing or decreasing the strength of 
the magnetic field. 

: c> 



Plate 4, Figure 170. 

The primary and secondary windings are secured to the 
iron core by means of wooden wedges, as per Plate 4. These 
wedges must be tight enough to hold the windings rigid. 
If the windings are loose, so that you can move them with 
your hands when the top casting is removed, then the wedges 
should be driven tighter. To do this it is only necessary to 
remove the top and slip some thin, blunt instrument down 
between the windings and the frame to the top of the wedges 


and drive them down further. Plate 4 shows the transformer 
with the top cover casting removed. To remove the cover, 
take out the four round head screws shown in Plate 2. 

The Edison transformer is claimed by its manufacturers 
to be practically noiseless in operation, and should it at any 
time become noisy there are three adjustments which may 
require attention: (a) The nut on top of the handle (crank) 
may have become loose. The screwshaft to which this 
handle is attached is fitted with a shoulder below the cast- 
ing, and between this shoulder and the under side of the top 
casting is a spring washer. It is necessary that the nut on 
top of the handle be set up sufficiently tight to compress 
this washer flat. This means the nut should be set up 
moderately tight, though, of course, not tight enough that 
the handle will turn too hard, (b) The leakage plugs are 
fitted at their sides with phosphor bronze springs. These 
springs hold the plugs rigid between the walls of the sup- 
porting guides. Should they fail of this purpose, then they 
must be bent to give greater tension, (c) The thread in the 
shaft to which the handle is attached should make a good 
fit in the crosspiece to which the plugs are fastened. A loose 
fit at this point will not make the transformer exactly noisy, 
but may cause it to hum. 

Operation. After connecting the transformer, close the 
line switch and the operating switch and strike the arc in 
the usual way, after which turn the adjusting handle until 
you get the desired result on the screen. This will, of 
course, vary with size of the picture, .etc. Under varying 
conditions it may be necessary to work with the handle 
clear down or clear up. Ordinarily, however, a position 
somewhere midway should meet the requirements. 


Power's Inductor, Fig. 171, consists of a well insulated, 
strongly clamped laminated core with the primary wound 
on one side or leg of the core and the secondary on the 
other. The casing consists of a cast-iron front and back, 
with a perforated brass cover. On the front, at the top, two 
wires emerge, underneath which, on the casting, is the word 
"lamp." These two wires connect directly to the carbon 
arms of the projector lamp. It makes no difference which 
wire you connect to the upper or lower carbon arm. At 
the back side, near the top, the two primary leads come out. 
They should be connected to the supply, as per Fig. 163, 



Page 351. On the face of the front casting is a hand-wheel 

which operates a single-pole knife switch, located on the 

I * | opposite side of the casting. When 

I I I I this switch is thrown so that its finger 

II j points toward "high" you are getting 
II j the maximum amperage, approxi- 
II jjf mately 65. When it points to "me- 

3 ? r"" T ^feAHfc^ I dium" you are getting a medium 

amperage, and when it points to "low" 
you are getting the lowest amperage 
the transformer will supply. 

The inductor is designed for a 
maximum of 65 amperes on "high," 54 
on '"medium," and 45 on "low" when 
used on 110 or 220 volts, it being, of 
course, understood that you cannot 
use 110 volt inductor on 220, or a 220 
on 110. In other words, you must 
have an inductor suitable to the vol- 
tage of your supply; also it must be 
Figure 1/1. suitable to the cycle of the current 

you use, though the inductor may be used on voltage rang- 
ing 10 per cent below to 10 per cent, above that for which 
it is rated, but in one case there will be a corresponding 
increase, and in the other a decrease in its rated amperage. 
The inductor is designed for a maximum temperature rise 
of 50 degrees Fahrenheit above the surrounding atmosphere, 
and ordinarily its temperature will not exceed 30 degrees in 
excess of the surrounding air. It occupies 12 x 14 inches floor 
space, is 19 inc'hes high, and weighs approximately 100 
pounds. Its efficiency rating will compare favorably with 
other machines of its kind. 


The "Hallberg" A. C. to A. C. economizer is nothing 
more or less than a transformer of the semi-constant cur- 
rent type, specially designed for use in moving picture 
projection arc circuits, taking A. C. at line voltage and 
delivering A. C. at .arc voltage. "Semi-constant" means 
that it will receive supply at a fixed potential, but will de- 
liver at the arc practically steady amperage flow, regardless, 
within reasonable limits, of the length of the arc. 

The device consists of a continuous, rectangular core, on 
one leg of which is wound a primary coil, and on the opposite 



leg a secondary coil, the latter being of larger, heavier wire 
than the former, to which the arc lamp is connected. 

In Fig. 165 we have a 
view of the top of the 
Hallberg Economizer 
showing the various 
taps coming out. The 
two marked "to lamp" 
are the terminals of the 
secondary coil, which 
attach, through fuses, 
to the arc lamp, as per 
Fig. 163. The terminal Figure 172. 

marked "1," Fig. 172, is 

the constant, and must always be connected to one side of the 
source of supply. Either one of terminals "2" "3," or "4," Fig. 
172, may be connected to the other side of the supply, according 
to the supply voltage and the amperage desired at the arc. 
Terminal "4" represents one end of the primary winding, 
of which terminal "1" is the other end. A, B, C are fuse 
receptacles, and leads "2" and "3" are taps connecting to 
the primary coil as per Fig. 154, Page 342. Now if a fuse plug of 
sufficient capacity to carry the primary current be placed in 
receptacle C, receptacles A and B being empty, then as you 
will readily see, the whole of the primary coil will be in use. 
This connection is designed for use where the primary voltage 
is a little above normal, or when you require the lowest am- 
perage the economizer will deliver. If the fuse be removed 
from C and placed in A, then several 
turns of the primary coil will be cut out, 
which will have the effect of boosting 
the secondary voltage, and hence the 
amperage at the arc. The fuse plug 
should be in receptacle A when the line 
voltage is a little below normal, or when 
the highest available amperage is de- 
sired at the arc. CAUTION: Do not 
unscrew the fuse plug while the arc is 
burning. If you do the current will arc 
and burn out your fuse receptacle ; other- 
wise this arrangement is cheap, practical, 
and should never give trouble. 
Fig. 173 shows the appearance of the Hallberg economizer. 
The machine table switch should always be on the line side of 
the economizer. 


Figure 173. 


The economizer is supplied for voltage ranging from 100 
to 120 and 200 to 220, and may be constructed for 25, 35, 40, 50, 
60, 120, and up to 140 cycles. The 110 volt economizer lines 
are usually connected to terminals 1 and 2 when the voltage is 
100 to 105; to 1 and 3 between 105 and 115, and to 1 and 4 
if between 115 to 120. If it be a 220 volt economizer then 
connect to 1 and 2 for 220 volt supply and to 1 and 4 for 240. 

The manufacturer supplies the following data for the Hall- 
berg economizer. 

Line fuses Line Line Line watts Amperes 

required. Voltage. Amperes. per hour. at arc. 

Regular Type 30-40 Amperes. 

20 110 18 1,400 30-40 

10 220 9 1,400 30-40 

Standard Type 45-55 Amperes. 

30 110 25 1,800 45-55 

15 220 13 1,800 45-55 

Special Type 60-80 Amperes. 

40 110 35 2,200 60-80 

20 220 18 2,200 60-80 

Searchlight Type 125-150 Amperes. 

80 110 75 4,200 125-150 

40 220 35 4,200 125-150 

There are four types of this device, viz: the "Regular," 
the "Standard," the "Special," and the "Searchlight." The 
Regular type is designed for stereopticon and very light 
motion picture theatre work, where the picture is small and 
the performance not continuous. 

The Standard type is recommended by the manufacturer 
for ordinary motion picture theatre performances. It delivers 
a maximum of approximately 60 amperes at the arc. 

The Special type is made for those who desire an amperage 
in excess of 60, and is size the author recommends to those who 
want brilliant screen illumination. 

The Searchlight type was ordinarily designed for Kinema- 
color work, but it is now offered to the regular motion pic- 
ture trade. It has a maximum capacity of 150 amperes. 

Where the Searchlight is used it is well to use either three- 
quarter or seven-eighth inch cored carbons. Where the 
Special and Searchlight economizers are used the asbestos 
covered cable should be No. 4 for the Special, and No. 2 
for the Searchlight. For all other economizers they should 
be No. 6. 



The Freddy Economizer, the general appearance of which 
is shown in Plate 1, manufactured by Walter G. Preddy, 
San Francisco, consists primarily of two parts, viz., a heavy 
laminated sheet metal core, 16 inches in length, around which 
is placed a winding consisting of two layers of No. 4 magnet 
wire. The first or inner layer is wound directly over the core, 
but insulated therefrom. The second, or outer layer is wound 
over the first, and has brass taps brought out on every 
seventh turn. These taps are so arranged that the windings 
may be tapped at eleven points, thus providing for a greater 
or less amount of inductance, according to the number of 
amperes it is desired to use at the arc. The taps are labeled 
"contacts" in Plate 2, the wire terminating in an arrow 
head, labeled "clamp," connecting to one of the contacts. 
The two-screw connection at the top of the coil, and the 
brass tap at the same end, are at the extreme ends of the 
windings, all other taps being interposed, and acting to 
cut in or out a certain number of turns of wire, thus varying 
the inductive effect, and hence the amperage at the arc. 

Plate 1, Figure 174. 

The Preddy Economizer is an economy coil, inductance coil, 
reactance coil, or choke coil, those names meaning the same 
thing and applying equally to the same apparatus. The 
more familiar term is choke coil. There are no switches or 
levers to manipulate; all the regulation is perfected by means 
of the clamp and contacts, Plate 2, as already described. 
The connector (clamp) is merely a slotted brass casting 
that slips on the taps, and is then screwed tight by hand. 
CAUTION: Never use pliers in making this connection. 

Directions. The Preddy Economizer is not a transformer 
or auto-transformer, and has no "primary" or "secondary" 



winding. It is connected into the arc lamp circuit precisely 
the same as you would connect a rheostat. See B, Fig. 142, 
in which just substitute a Freddy coil for rheostat C. It 
is advisable to use (manufacturer's recommendation) wire 
not smaller than No. 6, and fuses not smaller than 75 amperes. 
There is no reason for placing fuses on the lamp side of the 
Freddy Economy Coil, as is advisable with the transformer, 
since the amperage is the same on both sides of the Freddy 

Never attach the economizer to a metal lined wall unless you 
first remove the metal or place a marble or other insulating or 

Flate 2, Figure 175. 

non-metallic material of substantial thickness between the econo- 
mizer and the metal. If the device be attached to a metal 
lined wall or set on a metal lined floor there will be a vibra- 
tion set up in the metal, which will cause a more or less 
loud buzzing sound. The manufacturer recommends that 
fairly hard cored carbons be used in connection with this 
device, both top and bottom. The tap connection giving the 
highest amperage is the one opposite the tube connector. 



If a dissolver is to be used with one economy coil the two 
lamps must be wired in series. See "The Stereopticon." 

When using the economizer do not add rheostats to the cir- 
cuit, or switches for regulating, or other devices. Schemes 
of this kind often cause a great deal of trouble, for which 
the instrument gets the blame. 

The economizer is a very sturdily built, rugged device, 
Which ought to last indefinitely if given reasonable care. It 
is well insulated and will not "bake out," owing to the extra 
heavy insulation between the core and winding, as well as 
between the layers. 


The formostat, which is widely used and well liked on the 
Pacific Coast, and somewhat known throughout the Middle 
West, is of the auto type of transformer. Its ratio is two to 
one for 110 volt current and 4 to 1 in the 220 volt type that is 

Figure 176. 

to say, one ampere taken from 110 volt line becomes two on 
the secondary, while one ampere taken from the 220 volt line 
becomes four on the secondary. Its range of adjustment is 
from 30 to 65 amperes, and its construction is quite simple, 
there being two wires for the line and two for the lamp. 
These leads are marked with paper tags, when the formostat 


is purchased. In case the tags are absent the two large 
leads should be connected to the lamp and the two smaller 
one to the feed wires. The adjustment is made in divisions 
of about 4 amperes and without in any way disturbing the arc. 
In Fig. 176 we see a sectional front and side view, A and B 
being the line wires and 1 and 2 the coils. The regulation 
of amperage is secured by raising or lowering the top coil. 
In Fig. 177 we have a view of the formostat. At the top 
is a notched rack upon which hangs a wire loop; from 
this loop is suspended coil 1, Fig. 176. By lowering coil 1, 
a^^ ^^^ or in other words, drop- 

ping the wire loop to a 
lower notch in the rack, 
amperage is increased, 
or by raising it the am- 
perage is lowered. The 
winding on the 110 volt 
formostat is of No. 5 
wire, and as the instru- 
ment is of the auto type 
this is equivalent to two 
No. 5 wires in parallel, 
so that in fact each No. 
5 wire has only to carry 
32^ amperes. In the 220 
volt type the winding is 
of No. 4 and No. 8 
wires, and at full load 
the No. 4 carries 43 and 
the No. 8 17 amperes, 
respectively. A 110 volt 
formostat works well on 
any voltage from 105 to 
125; and the 220 volt 
177 machine operates suc- 

cessfully at from 210 to 
240 volts. The makers recommend that the formostat be placed 
on the floor under the lamphouse. Connect the wires marked 
"line," which are the smaller of the four wires, to the line 
through 30 ampere fuse and switch. Connect the two leads 
marked "lamp" directly to the lamp. The formostat makers 
recommend that there be no switch between the formostat and 
the lamp, but that it be placed on the line side. All wire con- 
nections should be soldered, unless some good type of wire 
connector is used; see D, Figure 30, Page 89. 



Wiring Diagrams for the Formostat. Fig. 178, No. 1, 
shows the connections used with the regular 110 volt formo- 
stat supplying two lamps alternately. No. 2 shows connec- 
tions used with 110 volt formostat for three lamps. That is to 

2 2.0 VOLT L//VE 

30 (\MP. SWTCH 


Figure 178. 

say, a motion picture arc and a dissolver. No. 3 shows con- 
nections used with special 220 volt formostat for two lamps, 
and No. 4 shows connections used with special 220 volt 
formostat for three lamps. 


The tags on the wires are marked A, B, C and D, in the 110 
volt type, and AA prime, B, , D, on the 220 volt tags. If 
it is desired to use the 110 volt formostat with connections as 
per No. 1 and 2, Fig. 178, the leads will first have to be 
selected by testing between the line and lamp leads with 110 
volt lamp. Between two of these wires will be found no 
voltage and these wires are line A and lamp C, therefore the 
two remaining are line B and lamp D. This test must, of 
course, be made with the current on. If it is desired to use 
connections No. 3 or No. 4, Fig. 178, with the 220 volt formo- 
stat, put out before the beginning of 1912, the wires will have 
to be changed, and this the manufacturer will do, free of 
charge. The change cannot be made outside of the manu- 
facturer's shop, and should not be attempted. 

Motor Generator Sets 

General Instructions. There are certain instructions 
which apply alike to all motor generator sets, rotary con- 
verters and other devices of like nature. To incorporate 
these instructions in the matter covering each individual set 
would consume valuable space needlessly, therefore, they 
have been incorporated under the head of General Instruc- 

General Instruction No. 1. Locating the Motor Gener- 
ator. In locating a motor generator or rotary converter, 
several things must be taken into careful consideration. 
Wherever practical it is much better to locate the machine 
either in the operating room or a room directly adjoining and 
connecting therewith. 

A basement, particularly if damp or dark, is objectionable 
for installations of this kind. Where there is dampness the 
insulation of the wires will absorb more or less moisture, 
which will be expelled rapidly when the machine warms up, 
and this, many times repeated, is likely to produce injurious 
results. The most serious objection is that in case anything 
goes wrong it takes much longer to investigate and make 
the repair, if a repair is possible, than it would if the machine 
were located in or adjoining the operating room. Still an- 
other objection to basement locating lies in the fact that 
basements are usually more or less dark, which entails the 
making of repairs and performing other operations entirely 
by artificial light. 


The only legitimate objection to locating machines of this 
kind in or adjoining the operating room lies in the possible 
vibration and noise or the weakness of the floor. 

As a general proposition it may be said that any floor too 
weak to carry a machine of this kind is unfit to be the floor 
of an operating room. Vibration can be, to all intents and 
purposes, eliminated by means of felt, as per instructions 
under "Installation." 

When practical, always set your motor generator out far 
enough from the wall so that you can walk all around it, 
and before your floor is put down have the conduits laid, 
so as to carry the connecting wires underneath the floor. 

This is a little extra expense and labor, but in the long 
run it pays, and pays big. 

If you do locate your generator in the basement it is a 
good plan to place it on a pedestal or platform raised some 
distance from the floor, particularly if there is any danger 
of the basement at any time containing water. The frame 
of the machine should be thoroughly grounded by means of 
a copper wire, one end of which must make good electrical 
contact with the frame and the other with a water pipe or 
the earth, as described under "Grounds," Page 259. Also 
select as light a spot as possible, if any daylight enters the 

If the machine is located in the basement, make your 
operating room leads of ample size. It won't cost much 
more, and there will be less waste. The size of the leads 
will, of course, depend on the amperage they are to carry, 
and their length. In this connection see Pages 42 and 45. 

General Instruction No. 2. Installation. As soon as a 
new machine is unboxed, the name plate should be carefully 
inspected. If it be a D. C. to D. C. machine, you have only 
to ascertain that the volts marked on the motor name plate 
correspond with your line voltage. If it be an A. C. to D. C. 
machine, then the volts, cycles and phase must agree with 
those of the circuit on which it is to be used. The name 
plate marking will also indicate the volts and amperes for 
the arc lamp, and due care should be taken that the am- 
perage rating, as indicated by the name plate, be not ex- 
ceeded to any considerable extent, except for short periods 
of time. 

If the motor generator is mounted on a sub-base which 
it is, for any reason, necessary to dispense with, great care 
must be exercised that the motor and generator be perfectly 


lined with each other, else there will be undue strain on the 
coupling of the two shafts. Failure to perfectly line the 
shafts will probably result in noise, vibration and a rapid wear 
at both the coupling and bearings. Machines in which the 
armature of the motor and generator are mounted on one 
shaft, with but three bearings, and no coupling between, 
should never under any circumstances be installed without 
their sub-base, if they are of the type that uses a sub-base. 
Where a motor and generator .are locked together, on a 
sub-base or otherwise, it is not necessary to bolt them 
down solidly to the floor (it is not necessary to build foun- 
dations for machines of this character), and if the machine is 
located in the operating room or in an adjoining room it is 
not desirable to do so. The best plan is: Have a sheet 
metal pan made, one to two inches deep and sufficiently 
large to contain the base of the machine and extend out 
under the oil boxes. Procure heavy felt the kind that is from 
one-half inch to one inch thick, if you can get it, and cut 
enough to make a pile at least 4 inches thick, cutting the 
pieces about 3 inches larger than the base of the machine. 
Place the felt where you propose to locate the machine, lay 
the pan on top of it and set the machine in the pan. No bolts 
or fastenings of any kind are necessary. If the machine does 
not set on the felt without giving trouble the armatures are 
not properly balanced and the machine should go back 
to the factory. The idea of the felt is to absorb all the 
vibration and prevent its being communicated to the floor 
and the walls of the building. It renders the machine to all 
intents and purposes noiseless. 

Caution. Where direct connected motors and generators 
are joined to each other by a flexible connection on the 
shaft, and not placed on a single, rigid iron base, then the pad 
proposition does not, of course, apply. Such an outfit must 
be bolted down on a solid foundation. After the machine has 
been on the pad a week, carefully level it, if necessary, by 
slipping sheets of metal under the low side. // is very necessary 
that the armature be perfectly level endwise, else it will not 
"float" (have end play), and failure to float will probably pro- 
duce grooved bearings and commutator. 

Having the machine located, revolve the armature by hand 
to make sure it revolves freely. Examine the armature and 
commutator carefully to see that they are not bruised. Let 
the oil out of the oil wells and fill them up with fresh oil. 
(See General Instruction No. 3.) The electrical connections 



should be made by an electrician, who should follow the 
wiring diagram sent with the machine. 

General Instruction No. 3. Oil. The much advertised 
patent oils are absolutely unfit for motor or generator lubri- 
cation. If you use them you are more than likely to either 
have trouble with the bearings, or a comparatively frequent 
and unecessary expense for bearing renewal, to say nothing 
of worn journals. 

The character of oil to be used will depend considerably 
upon climatic conditions. In the South, where it is always 
comparatively warm and much of the time summer heat, 
I would recommend the same oil used for generators in 
the local electric light plant. The 
superintendent of the plant will tell 
you what it is, and no doubt will sell 
you oil at a reasonable figure. You 
cannot do any better, because oil 
used to lubricate heavy generator 
bearings is necessarily an excellent 
lubricant, and you can rest assured 
the light plant has the oil best suited 
to local climate. In the Middle 
North, I would recommend a medium 
heavy dynamo oil for summer use; 
it may be used the year round if the 
generator is in a room that is kept 
warm in winter, but if in an unheated 
place a light dynamo oil will be 
found to give the best satisfaction in 
winter. In the extreme North a 
medium oil in summer and a light 
dynamo oil in winter will be best. 

Caution. Most, if not all, motor generator sets have the 
oil carried up to the journals by rings which rest on the 
journals and revolve merely by the friction of their own 
weight on the journal, as per Fig. 179, which shows the 
oil ring resting on the journal, revolving through a groove 
in the babbit bearing. Now, you will readily see that if too 
heavy an oil be used in winter time, and the machine be 
located where it is very cold, the oil will congeal and stop 
the ring from revolving, in which case no oil would be fed 
to the journal and there would be trouble. There are 
grooves cut in the babbit bearing to facilitate oil distribution. 

Be sure your oil is free from dust or sediment. Never 
leave oil standing open. If you do it will collect dust and 

Figure 179. 


the lubricating quality of the oil will be very greatly impaired. 
Dirty oil is often the cause of bearings heating. 

General Instruction No. 5. Cleanliness. It is important 
that all parts of motor generators be kept scrupuluosly clean. 
Oil should not, under any circumstances, be allowed to col- 
lect, either on the machine or on the floor near it, and the 
machine should, so far as possible, be kept free from dust. 
A medium size hand bellows will be found very convenient 
for removing dust from the armature, from around the pole 
pieces and in other inaccessible places. A dirty machine is 
evidence of a lazy, indifferent of incompetent operator. 

General Instruction No. 6. Loose Connections. It is 
highly important that all electrical connections and all bolts 
and nuts be inspected periodically and carefully tightened 
up, and all electrical connections be kept not only tight but 
perfectly clean. Loose connections are a continual source of 
absolutely unnecessary trouble. 

General Instruction No. 7. Ammeter and Voltmeter. All 
motor generators are or should be provided with both volt- 
meters and ammeters, and they should by all means be located 
on the wall in front of the operator as he sits in operating 
position. It is a serious mistake to install a voltmeter and 
ammeter in an out of the way place. They should be con- 
stantly under the operator's eyes, since there are points at 
which the arc furnishes maximum illumination with minimum 
current consumption, and with the ammeter directly in front 
of him the operator soon learns where he gets the most 
light with the least current consumption and, if he is a 
capable man, keeps his arc at that point. 

General Instruction No. 8. Care of the Commutator. The 
commutator of a direct current motor or generator ought 
to require very little care, but sometimes does require a great 

The best evidence the commutator is in Al condition is 
a sort of glazed appearance, smooth as glass, a brownish 
shade in color and a slight squeak from the carbon brushes 
when the armature is revolved slowly. To obtain and 
maintain this condition the following care must be given: 

(a) The brushes kept set as nearly as possible at the 
sparkless point, which point may, with the old style gener- 
ator lacking the inner or "commutator" pole, vary with the 
load. On the newer type of generator the inner or commu- 


tating pole is used and the manufacturer marks the point 
at which the brush yoke should be set by making either a 
chisel or center-punch mark on the yoke and on the frame. 
Some manufacturers fill these marks with white paint so 
they are very easily seen some do not. Where these marks 
are present the brush yoke should always be set so that the 
marks on the frame casting and the yoke coincide, or, in 
other words, are opposite each other! 

(b) The brushes must have just sufficient tension to 
make good electrical contact with the commutator, remembering 
that every particle of unnecessary pressure will tend to unduly 
wear both commutator and brushes, and to groove the copper 
unless the armature has a little end play. 

(c) That the commutator be kept clean and free from 
dust. This may best be accomplished by cleaning the whole 
machine every day, blowing the dust out from around the 
field poles, etc., with a bellows, and last of all, wiping off 
the commutator with a canvas pad made as follows: Cut 
a piece of ordinary canvas 6 inches square, fold this so 
that it is 2 inches wide by 6 inches long, which will 
form a pad with a face of one thickness, backed by two 
thicknesses. Next open up the pad and smear a little vaseline 
on the center section, which is the ^back side of the face of 
the pad, after which refold, let lie 'a few hours in a warm 
place, and it is ready for use. Sufficient vaseline will gradually 
soak through the pad to give the commutator all the lubrica- 
tion it needs, and that is mighty little. The foregoing 'holds 
good in summer, and in winter, too, if the generator is located 
in a warm .room, but if, on the other hand, the machine is 
cold, then it will be well to moisten the face of the pad by 
using a few drops of a very thin oil on a piece of glass, 
spreading it around evenly and then wiping it off on the face 
of the pad, the idea being to get the oil evenly distributed 
on the pad. Remember this, however, too little lubrication is 
better than too much, and heavy lubricants (thick oils) must 
never, never, NEVER be used on a commutator. If one applica- 
tion as above every six-hour run does not suffice, then it is 
likely that, (1) your brushes have too much tension, (2) 
your machine is overloaded, (3) your brushes not properly set 
or (4) there is some other trouble. Never use gasoline or 
benzine around a commutator; it is likely to attack and soften 
the shellac and insulation and thus set up serious trouble. 

Caution. Where the mica insulation of the commutator is 
undercut great care should be taken in regard to the lubricat- 


ing of the commutator, and if a soft brush is used no lubrica- 
tion should be given. This caution is necessary with under- 
cut insulation by reason of the fact that the lubricating 
medium will have a tendency to combine with carbon dust 
and fill up the space between the commutator bars, thus in 
time possibly short circuiting the bars. Also where soft 
brushes are used the brushes themselves as a rule contain 
sufficient paraffine to provide all necessary lubrication. 

(d) See to it that sufficient oil, or combined oil and carbon 
dust, has not collected at any point or spot, either on the 
commutator or face of any brush, to form a semi-insulation: 

(e) That there are no high or low bars and that the 
commutator is perfectly round. 

(f) That a fragment of copper does not drag across the 
insulation between two adjacent bars, or that oil and carbon 
dust does not form such a bridge. This fault will be evi- 
denced by a thin, sparkling ring of light around the commu- 

(g) That the brush springs do not carry sufficient current 
to heat them. 

(h) That the brushes fit properly in their holders, and 
are kept free from accumulation of dirt, dust, etc. They should 
be taken out and cleaned once in every 60 hours run. 

(i) That the brushes are neither too hard nor too soft. 

(j) That the armature "floats" slightly, i.e., has from one- 
sixteenth to one-eighth inch end play, according to size of 
machine. This tends to prevent the brushes from cutting 
grooves in the commutator; is very important. Unless the 
machine sets perfectly level the armature will not "float," hence 
a level setting is important. 

(k) That the copper and mica insulation wear down 

(1) That the generator is not overloaded, and that there 
are no other faults present which would tend to cause un- 
necessary sparking, or otherwise injure the commutator. 

Should the brushes of the motor or generator shpw 
excessive sparking, it might be attributed to one of the 
following causes; 

(a) If a belt driven machine, the belt may be slipping; 
if the sparking is spasmodic or intermittent, the trouble will 
probably be found in the belt, since belt slip causes sudden 



variations in speed, and this will, in itself, cause sparking, 
since it has the effect of producing heavy fluctuations in the 
voltage. The remedy, of course, is to tighten the belt, or 
use a belt dressing, and, in this connection, ordinary black 
printer's ink is as good an article as I know of to stop belt 
slipping, and ten cents worth obtained at any printer's will 
last for a month or more. 

Plate 1. 

Plate 2. 

Figur 180. 

(b) Brushes not set correctly, that is to say, the rocker 
arm too far one way or another; also the brushes may be 
too close together or too far apart. In the first case the 
remedy is to move the rocker arm until the neutral position 
is found, whereupon sparking will either cease or be reduced 
to a negligible quantity. If this fails to remove the trouble I 
would then see if the brushes themselves are the correct 
distance from each other. In a two-pole machine they should 
bear on the commutator at diametrically opposite points. 
That is to say, the distance from brush-point to brush-point 
should be exactly the same when measured both ways 
around the commutator; in other words, distance A should 
equal distance B, ,as per 1, Fig. 180. If it be a four-pole 
machine * with two positive and two negative brushes (four 
altogether) the correct distance to set them is one-fourth of 
the circumference of the commutator between the points 
of adjacent brushes, that is, distances marked X should all 
be equal, as per 2, Fig. 180. If it be a mc*chinv, with more 
than two positive and two negative brushes (more than 


four brushes all told), divide the number of commutator 
segments by the number of poles, or field coils of the machine; 
the result will equal the distance, in commutator bars, the 
brushes should be apart. 

(c) Dirty brushes or dirty commutator may cause spark- 
ing, and may even prevent the generator from picking up its 
load at starting, and will sometimes cause a badly fluctuating 
arc. Some of the causes of dirty brushes and dirty com- 
mutator are as follows: Carbon brushes contain a small 
amount of paraffine. When the carbon gets warm this par- 
affine, if excessive in quantity, is likely to ooze out and coat 
the commutator, thus partially insulating it in spots, or the 
paramne may mix with dust and coat the end of the brush 
with a semi-insulating compound. If copper brushes 
be used they may become clogged with a mixture of oil 
and dust; the obvious remedy is to clean the dirty parts. 
To clean the commutator, use a brush stiff enough to remove 
any foreign matter which may cling to the surface of the 
commutator, yet not stiff enough to injure the surface. If 
the brush will not remove the deposit,, then use 00 sand 
paper (never use emery paper or emery cloth on a commutator) 
applying the same while the commutator is revolving, but 
with just barely enough pressure to clean the metal. After 
having cleaned the surface, put a few drops of light oil 
on a cloth, or use the pad already described and hold it 
lightly to the commutator as it revolves. Don't get much 
oil on the surface of the commutator just a "suspicion," 
as it were. If it is a carbon brush which is dirty, or which 
does not fit the curve of the commutator, raise it just enough 
to slip a piece of fine sand paper (^ or No. 1) between the 
brush and commutator, with the sand side against the brush, 
and pull it back and forth around the curve of the commu- 
tator until enough of the brush has been ground away to 
clean the surface, or to make it fit the commutator. Be sure 
and always clean the commutator thoroughly after doing this, 
since if carbon dust is left adhering to its surface it may work 
into the insulation and cause a local short circuit between 
two bars. If the brush is made of metal take it out and 
clean it thoroughly with gasoline, trimming the edges and 
corners off with a file if necessary. 

(d) The brush not making proper contact with the com- 
mutator, which may be due to (1) tensioij spring not being 
strong enough; (2) tension spring having lost its temper; 
(3) brush stuck in its holder; (4) brush not fitting the curve 


of the surface of the commutator; (5) brush holder set at 
the wrong angle; (6) high bar or insulation. The remedies 
are: (1) Stretch the spring, if it is a spiral spring, or if it 
is not a spiral spring, do whatever is needful to make the 
spring stronger, installing a new one, if necessary; (2) put 
in a new spring, and, since the fact that the old spring 
has lost its temper is evidence that the spring itself is carry- 
ing too much current, reinforce it with a current-carrying 
jumper; (3) the remedy is obvious: do whatever is needed 
to loosen .the brush; (4) use sand paper, as before described, 
until the brush fits the commutator surface; (5) straighten 
the holder; (6) see section f, further on. 

There should, however, be only sufficient tension on the 
brush to insure its making good contact with the commutator. 
Be careful, therefore, and don't get your springs too strong. 
If you do there will be unnecessary wear both on the brush 
and the commutator, and this will to some extent add the 
element of mechanical heat generated by undue friction. 

The reasons for the brush sticking in the holder are: 
(1) Dirt in the holder or on the brush; (2) brush not true; (3) 
hammer that rests on the brush (where this type of tension 
is used) not working true on the slot-end of the brush. The 
brush should slip freely in its holder, though not freely 
enough to allow of any considerable amount of play, and 
the hammer should be so adjusted that it lies true in the slot 
at the end of the brush. A brush which is not true may be 
evened up by tacking No. 1 sand paper on a perfectly flat 
surface and rubbing tihe brush thereon. 

(e) Commutator worn too thin. If the commutator 
wears down too much, although it may wear evenly and 
appear to be in good condition, the brushes will spark in 
spite of everthing you may do, particularly when the machine 
is working at capacity. The reason might lie in the fact that 
since the segments are wedge shape, as they wear down they 
become narrower, thus allowing the brush to span more of 
the circumference of the commutator than was intended, or 
there might be a slight error in the setting of the brush 
holder, and this error becomes greater as the distance 
between the brush holder and the commutator increases. 
The only remedy is a new commutator, but the sparking 
may possibly be lessened somewhat by moving the brush 
holder closer to the commutator. This trouble appears at 
its worst in a series type machine. 

(f) A high or low commutator segment. This fault may 


usually be detected by the clicking sound made by the brush 
in passing over the defective segment. When the segment 
is low the brush rides in toward the shaft each time the bad 
bar passes under it. If it is high the brush will jump. The 
remedy will depend somewhat upon the cause. It may be 
that the segment has become loose, in which case the bar 
may be driven back into place by tapping lightly with a 
wooden mallet, or by using a wooden block and hammering 
gently, but the armature will probably have to be taken 
out and sent to the repair shop, unless you yourself can 
tighten the clamp ring a rather delicate operation. If the 
segment is high by reason of the fact that, being of harder 
material than its mates it has worn down more slowly, then, 
using a fine file it may, with great care, be dressed down. 
If, on the other hand, it is low, then the only remedy is to 
turn down the rest of the bars to match. If the fault is 
slight this may be done by re'moving the brushes and holding 
a piece of grindstone which has been turned out to fit the 
circumference of the commutator to it while it is revolved 
rapidly. This process is, however, slow. The best way is 
to put the armature in a lathe and turn it off. The grinding 
may, in the case of a motor, however, be done with the 
brushes down and the machine running by its own power, 
but if this is done it should be done with great caution. 
When you are through the face of the brushes should 
be thoroughly cleaned by drawing No. J^ sand paper 
around the curve of the commutator with the sand side 
next to the brushes in order to grind off their face, and 
thus remove any particles of sand which may have become 
embedded in the brush, since it would scratch the commu- 
tator and cause undue wear. It is better to do the grinding 
with the brushes raised and the machine run from some 
outside source of power where it is practicable. 

(g) A rough or eccentric commutator. This may be 
caused by improper care, or by the use of defective materials 
in its construction. A rough commutator may be detected 
merely by feeling. The mica insulation between the seg- 
ments will either stand out in ridges, or be worn down so 
that there is a small groove between the segments. An 
eccentric commutator may most readily be detected by hold- 
ing some instruments firmly against the frame opposite the 
commutator, so that its ends just touch the bars. If the 
commutator is true it will touch all the way round as the 
armature is slowly revolved, but if the commutator is eccentric 
it will, of course, only touch the high spots. If the eccentric 


be bad it will cause the brushes to move in and out of their 
holders perceptibly when the armature is revolved slowly. 
The only remedy is to turn the commutator down, and this 
can only be sucessfully done in a machine shop where work 
of this character is understood. 

(h) Brushes having too high resistance, the evidence of 
which is that they get very hot and slowly crumble away 
at the end next to the commutator. The remedy is to get 
good brushes. 

(i) Low bearings. In some types of machines low bear- 
ings will throw armature out of center sufficiently to distort 
the magnetic field, and this will cause sparking. The evi- 
dence of this fault is that the air gap between the armature 
and the pole piece will be smaller at the botttom than at the 
top. The only remedy it to replace the worn bearings with 
new ones. 

(j) A short-circuited armature coil. This trouble will 
cause the voltmeter to fluctuate badly, and the shorted coil 
to heat very quickly. The coil may be shorted within itself, 
or there may be a connection between two adjoining com- 
mutator segments. Remedy: locate and remove the short. 

(k) A reversed armature coil. This may be located by 
holding a compass over each coil of the armature in turn, and 
sending a direct current through the coil, with the brushes 
raised and resistance in series; or current from a battery 
may be used. The coil which causes the compass to turn 
in the opposite direction from its mates is the guilty party. 
The remedy is, reverse the connection or direction of the 
windings of the defective coil. 

(1) A bent armature shaft. This, of course, will cause 
the whole armature to wobble. The only practical remedy is 
a new shaft. 

(m) Overload. The most prominent symptom of over- 
load is the armature heating all over. Sparking may be 
lessened, but not entirely stopped, by moving the brushes 
aihead or 'back. By "ahead" I mean in the direction in which 
the armature is revolving. The remedy is obvious. Get a 
machine of larger capacity, or cut down the load on the one 
you have. 

(n) High speed sparking is caused by the brushes not 
being able to make proper connection with the commutator by 
reason of excessive armature speed. 

(o) A weak field. This may be detected in a generator 
by its inability to pick up readily, and by failure to maintain 
normal voltage. On a motor the starting power is decreased, 


but the speed and current are increased. A weak field may 
be caused by (1) a loose joint in the magnetic circuit; (2) 
heat may lower the insulation of the field winding sufficiently 
to allow the current to short circuit through it; (3) there 
may be a metallic short in the field coil. Remedies: With 
at voltmeter test across each field coil; the one showing 
the least drop is the defective one. If all read the same, 
then there is a loose joint in the magnetic circuit. 

(p) A shaky foundation, or anything else that causes 
vibration in the machine will set up commutator sparking. 
The only remedy is to eliminate the vibration. 

Should a ring of fire develop, or something that looks like 
a ring of fire, around the commutator, it may be caused by 
(a) a piece of copper pulled across the insulation between 
two bars: (b) an open circuit in the armature. 

In the first instance the ring will not be strong, but just 
a thin sparkling streak of light around the commutator. The 
remedy is to remove whatever is causing the short between 
the bars, which can usually be done by holding a piece of 
fine sand paper lightly to the commutator, though the right 
way is to stop the machine and hunt up the trouble, using 
a magnifying glass if necessary. An open circuit in the 
armature, however, might be caused by reason of a break in 
one of the armature wires itself, or in one of its connections 
with the commutator, and these in turn may be caused 
by excessive current burning off one of the wires, or a nick 
in one of the wires may be the seat of the trouble, or the 
commutator may become loosened and break off one or 
more of the leads. The defect may be readily located, as 
the mica will be eaten away from between the commutator 
segments to which the faulty coil is connected, and the 
segments themselves will become full of holes and burned 
at the edges. If this trouble is caught in time the open may 
be closed and the commutator turned up true. Sometimes, 
by reason of carlessness, abuse or overload, the armature 
becomes hot, and this causes the solder on the connections 
between the coils and* commutator bars to soften, where- 
upon centrifugal force will throw it out, and there will, of 
course, be trouble, though there is no complete opening of 
circuits'. The action, however, so far as the ring of fire be 
concerned, is the same as if there were, and the commutator 
bars will become blackened and pitted and their edges 
burned. But if any of the foregoing faults be caught in 
time they can be remedied; if not it will be necessary to ' 


install a new commutator, and perhaps a new armature coil 
as well. 

General Instruction No. 9. Before starting the machine 
see that it is perfectly clean and that the brushes move 
freely in their holders and make good contact with the com- 
mutator. Also make sure that all connections are tight. 

General Instruction No. 10. Bearings Run Hot. The first 
rule when a bearing runs hot is to see that the oil well is 
filled with good clean oil and that the oil-rings run freely, 
carrying the oil to the shaft. If the bearing runs hot on 
a new machine shut down and wash out the bearing with 
kerosense. Trouble is probably due to dirt that has accumu- 
lated in shipment. If the bearing has been running along 
satisfactorily and suddenly gets hot, flood the well with 
clean oil, leaving the drain cock open and pouring in the 
clean oil while the machine is running to free the bearing 
from dirt. A change to a different grade of oil, either 
heavier or lighter, will often correct a bearing trouble of 
this kind. NEVER USE WATER TO COOL A BEARING, it may get 
into the insulation of the windings and cause a worse trouble. 
A machine with clean oil of the proper grade never gives 
trouble from hot bearings. 

General Instruction No. 11. Heating. Many operators who 
are handling motor generator sets and find them getting 
rather warm become unduly alarmed. Excessive heat is, of 
course, not only bad, but dangerous to the insulation. How- 
ever the fact must be taken into consideration that the 
temperature of operating rooms frequently reaches between 
35 and 40 degrees Cent. The American Institute of Electrical 
Engineers allows a temperature rise of 50 degrees Cent. (90 
degrees Fahr.) above surrounding atmosphere, this being 
based on 40 degrees (72 degrees Fahr.) atmospheric temperature. 
Therefore, simply because, in a hot operating room one 
cannot hold his hand on the iron of the machine with com- 
fort, it does not follow that the temperature is dangerous. 
A thermometer ought always to be used to determine such mat- 
ters. If the thermometer does not register a temperature rise of 
say more than 30 or 35 degrees above the surrounding atmos- 
phere (Centigrade), you need have no uneasiness. To change 
Centigrade temperature to Fahrenheit temperature multiply 
the degrees Cent, by 9/5 and add 32. For instance: opera- 
ting room temperature, 40 Cent. What is it Fahr.? 40X9/5 
= 40-4-5 = 8X9 = 72 + 32=104 degrees Fahr. 



General Description. Both A. C. to D. C. and D. C. 

to D. C. compensarcs are what are commonly styled "motor 
generator sets," that is to say, two machines coupled to- 
gether, one being a motor and the other a generator. In 
the A. C. to D. C. compensarcs the motor and generator are 
mounted on a common base, as shown in Plate No. 1. 
Fig. 181. The motor and generator frames of the D. C. to 
D. C. compensarcs are, however, coupled together by a 
common flange, as shown in Plate No. 2, Fig. 181, so that 
no base is necessary. All Fort Wayne compensarcs are 
shipped completely assembled, and require only proper in- 
stallation, filling of the bearings with oil and proper elec- 
trical connection to the supply and lamp circuits (See 
General Instruction No. 2, Page 369) before putting into 

Plate 1. Plate 2. 

Figure 181. 

The A. C. to D. C. compensarc consists -of a standard 
induction motor, either single, two or three phase, the same 
being directly connected to a special D. C. generator. The 
armature shafts of the set are joined by couplings, and 
there are but three bearings, two on the motor and one on 
the generator. The generator end of this set is wound 
specially for use with projection arc lamps, and the winding 
is such that no steadying resistance is necessary between 
the arc and generator. 

While the 115 and 220 volt D. C. compensarcs are commonly 
referred to as "motor generator sets," rightly speaking they 
are not, since electrical connections are different from 
the true motor generator set. The machine is in effect a 


"balancer." The 500 volt D. C. compensate is, however, a 
true motor generator, the motor having no electrical con- 
nection with the generator. The generator end of the D. C. 
compensarc has exactly the same characteristics, as that of the 
A. C. to D. C. machine, and will handle the arc without 
any steadying resistance interposed. The two-lamp outfits 
use a steadying resistance during the time of changing from one 
lamp to the other only, during which period both arcs are 
burning simultaneously. The generator end of both A. C. 
to D. C. and D. C. to D. C. compensarcs have practically 
the same mechancial construction. 

The D. C. compensarc has a fan, protected by a metal 
guard for the safety of the operator, mounted on the shaft 
between the two machines. This fan rotates with the shaft 
and sets up a current of air which helps keep both motor and 
generator cool. 

Installation. See General Instruction No. 2. 

Oil. See General Instruction No. 3. 

Removing Sub-Base to Install. See General Instruction 
No. 2 and, in addition, dowel pins are provided in the base 
of the generator end. To remove these pins hold the squared 
head of the pin with a wrench and tighten up the nut, which 
will pull out the pin. Be very careful that any liners found 
under the feet of the motor- or generator be carefully replaced 
in their original position. Should the coupling be taken apart 
it must be very carefully reassembled, making sure that the 
chisel marks on the rim register with each other. 

A. C. to D. C. compensarcs should never be run on circuits 
where the variation of either frequency or voltage from normal 
exceeds 5 per cent. Where both frequency and voltage vary the 
sum of the variation must not exceed 8 per cent. 

Size of Fuses. The lamp side of these machines does not 
require fusing, since the generators automatically protect 
themselves against overload current when the arc is short 

The motor side of the various machines should be fused as 

D. C. Compensarcs. 

50 amp. 1-lamp and 

2-35 amp. lamps 2-50 amp. lamps 

35 amp. 1-lamp alternately alternately 

115 volt 30 amp. fuses 60 amp. fuses 100 amp. fuses 

230 volt amp. fuses 40 amp. fuses 60 amp. fuses 

550 volt 10 amp. fuses 20 amp. fuses 30 amp. fuses 


A. C. Compensates. 

35 amp. 1-lamp 

50 amp. 1-lamp and 
2-35 amp. lamps 

2-50 amp. lamps 

125 amp. fuses 
60 amp. fuses 
60 amp. fuses 
30 amp. fuses 
50 amp. fuses 
30 amp. fuses 

The wires should be of sufficient size so that the line 
drop from the machine to the lamp will not exceed one 

Single Phase 
110 volt 35 
Single phase 
220 volt 20 
110 volt >20 
220 volt 10 
110 volt 20 
220 volt 1 2 






Plate 3. 

Plate 4. 

Figure 182. 

volt (see Page 45) or 2 per cent, of the voltage when the 
machine is delivering full load current to the lamp. If 
wires of too small diameter be used the lamp will be robbed 
of some of its amperage and give poor light. 

Electrical Connections. The D. C. to D. C. Compensarcs 
for 115, 230 and 500 volts, one lamp outfits, are connected as 
shown in Plate No. 3, Fig. 182, while those for the two 
lamp outfits are connected as shown in Plate No. 4, Fig. 



182. The connections for the A. C. to D. C. two lamp com- 
pensarc is shown in Plate No. 9, Fig. 183, while those for the 
one lamp outfits are connected as shown in Plate No. 8, 
Fig. 183. 

Plate 8. 

Plate 9. 

Figure 183. 

Internal Connection Diagram, 115-230 Volt 
D. C. to D. C. Compensarc. 

Plate 12, Figure 184. 


The diagrams shown in Plates 3, 4, 8, and 9, which are 
the external connections for the different types of compens- 
arcs, are practically the only ones the operator will have 
occasion to refer to, since all internal connections are care- 
fully made before the machine is tested at the factory, and 
are as they should be when the operator receives the machine. 

Internal Connection Diagram, 500 Volt 
D. C. to D. C. Compensate. 

Plate 5, Figure 185. 

It is only in exceptional cases that some trouble inside 
the machine necessitates the opening of the internal con- 
nections. In such cases Plates 5, 6, 7, and 12 should be 
referred to in reconnecting. 

It is recommended that one of the steel panel switch- 
boards, Plate 10, especially designed for use with the com- 
pensarc, be included in each compensarc installation. It will 
not only facilitate the wiring of the set, but help serve the 
purpose of General Instruction No. 7, which see. 

Starting D. C. to D. C. Compensates. To start the D. C. 
to D. C. compensarc, with projection machine switch open, 
close the switch in the main line, whereupon armature will 
begin to slowly rotate, in a counter-clockwise direction as 
you face the generator commutator. Proper direction of rota- 
tion is, indicated by the small arrow on the bearing housing. 


Next move lever of starting box slowly to right as machine 
speeds up, until it finally reaches the last contact, where it 
will be caught and held by the cut-out magnet. By this time 
the armature will have reached maximum speed. 

The field rheostat of the generator field circuit is marked 
with a small white arrow to indicate proper position it should 
occupy for machine to deliver the current and voltage at the 
arc as shown on generator name plate. 

To Start Arc. When the armature is up to speed, arc 
may be struck as follows: Close projection machine switch 
and bring carbons of lamp together, instantly separating them 
again about one-sixteenth of an inch, gradually increasing this 
distance as the carbons heat up until the proper length of 
arc to supply maximum screen illumination is reached, 
whereupon the voltmeter should register about 55 volts at 
the arc and the ammeter about 35 amperes, where the 35 
ampere set is used, or 55 volts at the arc and 50 amperes 
if it is a 50 ampere outfit. 

Caution. The closing of the carbons short circuits the 
generator, and, of course, instantly creates an overload. The 
generator is wound to protect itself against this very thing, and 
unless the carbons are instantly separated the generator will 
lose its voltage- This does no harm to the machine, but it 
will be necessary to separate the carbons for perhaps ten sec- 
onds until the voltage again reaches normal, zvhereupon the arc 
may be struck in the usual manner. 

As the machine warms up it may be necessary to move the 
handle of the rheostat one or two buttons away from the 
mark, to the left, in order to maintain the desired voltage and 
amperage at the arc. 

Reversing Connections. Provided the circuits have been 
connected as shown in the diagram the polarity will be as 
indicated, and the upper carbon of the lamp will be positive. 
Should an error be made in connections, and either or both 
the voltmeter and ammeter read backward, the trouble must 
be corrected. Examine all diagrams and see that all con- 
nections are made in accordance therewith, particularly that 
the motor terminals are connected to the proper side of the 
line. Do not attempt to correct trouble by reversing the 
terminals at the generator. The machines are all carefully 
checked up complete with their equipment when tested, and 



the motor must, therefore, be connected to the proper side 
of the line in order to bring the polarity of the voltmeter 
and ammeter of the projection lamp right. 

One-Lamp Outfit. 
Plate 6. 

Two-Lamp Outfit. 
Plate 7. 

Internal Connection Diagram A. C. to D. C. Compensarcs. 
Figure 186. 

The operation of the two-lamp-alternately equipment is 
the same as for the two-lamp-alternately A. C. to D. C. 

Starting A. C. to D. C. Compensarcs. In starting A. C. 
to D. C. Compensarcs, see that the projection lamp switch 
is open. If the motor is single phase, close the main line 
switch and move the starting box arm from "off" position to 
the split segment, which will put into action the number of 
starting coils necessary to cause the armature to rotate. 
When the armature has attained nearly full speed, the arm of 
the starting box should be moved quickly over to the last 
segment where it is held by a latch controlled by a 
relay magnet. Should the voltage at any time fail, the relay 
magnet will release the latch, allowing the starting arm to 
automatically return to the "off" position, thus protecting 
the motor armature from damage in case the voltage comes 
on again. 


The two and three phase outfits do not require starting 
boxes, but should be equipped with double-throw starting 
switches which have only one side fused. When starting up 
the switch should first be closed to the unfused side. When 
the speed of the armature reaches normal the switch should 
be quickly thrown over to the running (fused) side. When the 

Plate 10, Figure 187. 

speed of the motor reaches normal, the starting box handle 
or the double-throw switch in running position, and the 
rheostat handle set as indicated by the white arrow, the 
projection machine switch may be closed and the arc struck 
as described under "Starting D. C. Compensarcs." 

The coupling between the motor and generator is marked 
to show the direction in which the armature should revolve. 
It should run clockwise as one faces the generator commu- 
tator. The direction of rotation of two-phase induction 
motors may be reversed by interchanging the two stator 
leads of the same phase. In the case of single or three phase 
motors it is only necessary to interchange any two leads. 

Operating Directions for Two-Lamp Outfits, both D. C. to 
D. C. and A. C. to D. C. The motor of the two lamp 
outfits is started the same as the regular single-lamp outfits, 
directions for which have already been given. 

Have change-over switch (by change-o ( ver switch the 
single pole double contact switch is meant) on the panel 
closed, and start the first lamp by closing the switch and 
striking the arc in the usual manner. When it is desired 
to change from one lamp to the other, open change-over 
switch while the first lamp is still burning, then close the 


projection machine switch of the second lamp and strike 
its arc. Open the projection machine switch at the lamp 
which is to be cut out, and then close the change-over 
switch. By tracing the connections in Fig. 182 and Plate 
9 it will be seen that when the change-over switch is opened 
the current must flow to the lamp which is burning, and 
must pass through grid resistance, which has the effect 
of steadying the arc and preventing it from going out at 
the instant the arc is struck at the second lamp. It is 
therefore possible to strike the second arc and burn the 
crater into proper shape while the end of the first reel is 
still being projected, and to accomplish the effect of dis- 
solving one picture into the next. The steadying resistance 
is only in circuit when both lamps are burning, and care 
must be taken that the change-over switch is kept closed 
when only one lamp is burning. If, for any reason, an 
increase in current is needed at the arc, or it is necessary 
to heat up the carbons very quickly, the change-over switch 
may be opened on one lamp for a few minutes, thus in- 
creasing the current in the arc without disturbing the field 
rheostat setting. 

Caution.. Keep the first arc rather short at the instant the 
second arc is struck. 

If this is done neither arc will go out, or even flutter 
during the period of lighting the other arc. The ability to 
handle both arcs perfectly and change over without a 
flicker in the picture is soon acquired, and if the second arc 
is started long enough ahead to be perfectly steady there 
is no difficulty in dissolving one picture into the next 

Caution. Care must be taken that the two lamps are not 
burned longer than is really necessary, since the compensarc is 
not intended to carry both lamps continuously, neither has it 
the capacity to do so. 

With one lamp burning the ammeter will show from 35 
to 50 amperes, and the voltmeter about 55 volts; when both 
lamps are burning the ammeter will show approximately 
70 to 100 amperes and the voltmeter 70 to 75 volts, the 
voltage being automatically increased to compensate for the 
drop in the grid resistance. The voltmeter, as shown in 
the diagram, Plate 4, is connected across machine terminals 
1 and 3 and indicates the machine voltage, which is the 
same as the arc voltage when the change-over switch is 


Care of Machine. Cleanliness. See General Instruction 
No. 5. 

Oil. See General Instruction No. 3; also, in addition, 
immediately after starting a new outfit raise the bearing 
caps and see that the oil rings are revolving freely and 
carrying oil up to the top of the shaft. Keep the oil to 
the proper level in the well, which is nearly to the 
lip of the overflow oil gauge. The oil wells should be 
cleaned out occasionally and new oil supplied. They should 
invariably be filled through the side filling hole and not 
through the top of the bearing. If filled through the top 
the oil is likely to run out through the ends of bearings, 
get into the windings and do damage. 

Bearings. As soon as the bearing linings become worn 
so that the armature is in danger of rubbing against the 
stator, a new set of bearing linings must be inserted. To 
remove the bearings first take out the set screws in the 
bearing-housing. Having done this lift the oil rings up so 
that they clear the bearing lining; to lift rings use a wire 
with a hook bent on one end and raise rings with wire 
through the bearing cover and drive out the bearing linings 
with a wooden block of the same diameter as the bearings 
themselves. The bearings are so made that they fit the hole 
in the housing snugly enough to require light driving to 
seat them, and they must be handled carefully and intelli- 
gently. When duplicate bearings are supplied for the alter- 
nating current motor the set screw depression is already in 
the bearing, but the D. C. motor generator bearings, which 
regulate the end play, are supplied without the spot for 
the end of the set screw and they must be spotted before 
being put into place. Use a three-sixteenth inch drill and 
drill a spot for the tip of the set screw the same distance from 
the end of the bearing as the one being replaced. 

Care of Commutator and Brushes. See "General Instruc- 
tion," No. 4, and in addition, to secure proper commutation 
and proper operation the brushes must occupy the correct 
position on the commutator. The proper position of the 
brush has been determined at the factory, and is indicated 
by chisel marks, filled with white lead, on the brush yoke 
and frame. 

// is very important that these marks be in line with each 

Should the brush holders become loosened or moved in any 




Direction of 
Plate 11, Figure 188. 

way they must be carefully reset so that they may make 
proper angle with the commutator, as shown in Plate 11. 
They must also be so placed around the commutator that 
the distance from tip to tip of the brushes is exactly the 
same when measured both ways around the commutator. 

See Fig. 180, Page 375. Care 
should be taken that the brush 
holder be securely fastened at an 
even height, one-sixteenth of an 
inch above the commutator. It is 
recommended that an extra set 
of brushes be kept on hand. 
Brushes may be worn down to 
approximately three-quarters of 
an inch in length. Only brushes 
of the proper grade will give 
satisfactory results, therefore only 
the brush furnished with the 
machine or others exactly the 
same grade should be used. 

Loose Connections. See "Gen- 
eral Instruction" No. 6. 
Loose Connections. See "General Instruction" No. 6. 
Trouble. All compensarcs are carefully inspected at the 
factory and tested on a projection arc lamp under actual oper- 
ating conditions, as nearly as they can be secured in a factory, 
therefore when the machine is received by the operator it 
is ready to set up and run. If trouble is experienced do not 
blame the machine until you are certain it does not lie in 
some part of the equipment or in some local condition. 

Ordering Repairs. If it is at any time necessary to order 
repair parts, such as new brushes, new bearings, etc., bear 
carefully in mind the fact that the serial number and name plate 
readings of the machine must be placed on the order. 

D. C. Compensarcs. Machine will not start: If the ma- 
chine does not start first examine the fuses and make sure 
that the power is on at the switch terminals. Then trace 
and inspect the connections from the switch through the 
starting box, armature, brushes, field and back to the switch, 
and an opening in the circuit will probably be found. 

Fuses Blow: If the fuses blow make sure they are of 
proper size for the amperage used, and not loose in their 
contacts. Examine the starting box for grounded or short 
circuited resistance coils. Look inside the machine and see 
that the connections are not touching inside where they are 


not easily seen. See that the brush yoke and housing marks 
agree, to insure that the brushes are set in same position as 
when adjusted at the factory. Look all around the commu- 
tator at the connections between the armature windings and 
the commutator bars. Such minute inspection should locate 
the trouble. 

A. C. to D. C. Compensates. Machine does not start: If 
the machine does not start when the switch is closed, first 
examine the fuses and make sure the current is on at the 
switch terminals. It sometimes happens that a single fuse 
has blown on a three-phase three-wire outfit, in which case 
the compensarc will run as a single-phase machine, but if 
stopped will not start again until the blown fuse has been 
replaced if a single throw switch be used. However, if a 
double throw starting switch be used the compensarc will be 
started up on the unfused side. Therefore, the missing fuse 
must be detected by the operation of the machine while 
running. If a fuse is missing it can usually be detected by 
the unusual noise made by the machine while running, by 
the motor end heating excessively, and more particularly 
by change in speed with change in load, and general un- 
steadiness of the arc. If a fuse be blown it should be re- 
placed immediately, else it may cause the burning out of 
the motor. 

D. C. and A. C. to D. C. Compensates. Sparking at the 
brushes: When a vicious sparking develops under the 
brushes of the compensarc it is an indication that something 
is radically wrong. The most usual causes are dealt with 
fully under General Instruction No. 8, Page 372. In addi- 
tion it may be noted, however, that in removing the brushes 
from the boxes for cleaning, which should be done once a 
week, do not take the pig tails loose front the brush holders, 
and be sure to place the brushes back in the boxes in their 
original position, for if they are turned around they will 
not fit the commutator surface. The brushes should have a 
smooth, unscratched surface, free from any copper deposit. 

Open or Short Circuit in Armature: This trouble will most 
often occur where the armature winding is connected to the 
commutator, and results generally from a bruise in handling, 
from some foreign body getting caught in the armature, or 
from a chip caught when the commutator is being turned 
or repaired. If an open circuit the trouble is very apparent, 
since the long heavy spark accompanying it generally eats 
away the mica between the segments on each side of the 
break, thus indicating its location. A short circuit in the 


armature will show at once by the excessive heating, and 
perhaps smoking of .the coil or coils short circuited and if 
the machine is continued in operation it will be burned out. 
Where trouble of this kind is suspected the necessity of 
prompt attention by an electrician is obvious. 

Overload: If considerably more current is being taken by 
the lamp than the machine is designed for, sparking may 
result. See that the machine is not excessively overloaded. 

Brushes in wrong position: If the brushes are left in the 
same position as when the machine is received, trouble will 
not occur from this cause. If brushes are ever moved or 
changed, see that they are put back where they belong, 
and that marks on brush yoke and bearing housing agree. 

Machine makes excessive noise: This is most often due 
to a weak floor, or to the machine not setting firm and 
level. If the noise seems to be in the machine itself, and 
nothing can be observed out of place, send for an electri- 
cian, as the trouble may be serious. 

Bearings run hot: See General Instruction No. 10. 


(1) Keep the machine clean. 

(2) Keep the oil wells full (not overflowing) of good 
clean lubricating oil. 

(3) Keep the commutator and brushes free from gum and 

(4) Keep contacts clean and tight. 

(5) Keep lamp and wiring free from grounds. 

(6) Keep the current at the arc within the rating of the 

When repair parts are needed it is poor economy to try to 
get along without them. Brushes and bearings for these 
machines can be shipped on short notice and will always 
be of correct size and quality. In ordering from the manu- 
facturer simply give the nameplate marking, serial number, 
etc., and no difficulty will be experienced in promptly secur- 
ing the desired parts. 



The Wotton Vertical Rexolux 

THE Wotton Rexolux is a new, vertical motor generator 
set, manufactured by the Electric Products Company, 
Cleveland, Ohio, designed particularly for motion pic- 
ture work. The word "Rexolux" is a trade name meaning 
King of Light. 

This machine is a vertical motor generator set, converting 
alternating current of standard line voltage into direct 

current at arc voltage. The 

machine is built vertical with 
a view of allowing its installa- 
tion in the operating room, even 
when space is limited, thus 
placing the machine directly 
under the eye of the operator; 
also, the vertical design permits 
of a rugged form of construc- 
tion which tends to reduce vi- 
bration and noise to a minimum; 
also it makes the machine very 
accessible and easy to assemble 
and disassemble. 

The Rexolux is built in three 
sizes, viz: a machine designed 
to operate a single projection- 
arc lamp; a machine to operate 
two lamps alternately, and one 
to operate two lamps continu- 
ously. Where two lamps are 
operated continuously only the 
70 ampere machine is available. 

Tihe 50 ampere machine, of 
either the M, MA, or MMA type 
(the meaning of these different 
types will be explained later 
on), occupies a floor space 17 
by 20 inches, and has a vertical 
height of 34 inches to the top 
of cap 14, P. 1. The switch- 

Plate 1, Figure 189. 

board, supported by angle irons, is immediately over the 
machine, so that the entire space required for the 50 ampere 
equipment is 17 by 20 inches on the floor, by 5 feet in vertical 
height. The 35 ampere machine is 3 inches less and the 70 



ampere is 3 inches greater in height, but the* floor space 
required is practically the same for all the types. 

In referring to the ampere capacity of the above machines, 
the ratings are based on continuous operation. The 35 am- 
pere machine will carry SO amperes, the 50 ampere machine 
80 amperes and the 70 ampere 140 amperes for short periods 
of time, meaning by this that these machines will carry full 
load continuously, and stand the overload named for short 
periods, say not exceeding two or three minutes. 

These machines are built for all standard voltages and 
frequencies, viz: 110, 220, 440 and 550 volts; 25, 30, 40, 50 and 
60 cycles, single, two and three phase. 

Construction. Referring to Plate 2, Fig. 190, it will be 
seen that the machine consists of four main castings, viz: 
base casting 20, which rests directly on the floor, and con- 

Plate 2, Figure 190. 

Iff - 
tains in its center the cup or depression carrying ball race 6, 

which supports the entire armature; casting 18, which rests 
on base 20 and forms a housing for the alternating! cur- 
rent driving motor, the detailed construction of the wind- 
ings of which are plainly seen at 19, Plate 2; main upper 
casting 7, which supports the pole pieces of the D. C. gen- 
erator, and upper yoke casting 11, carrying grating 23, the 
upper armature bearing, and cap 14, Plate 1; main upper 
casting 7, Plate 2, and yoke castings 11, Plate 2, are held 
together by bolt 27, Plate 2, dividing at the dotted line. 
The armature stands vertical (on end), with the rotor of 



the alternating motor, 4, Plate 2, below, fan 5 above rotor 
4, and armature 1 with commutator 2, above the fan, the 
upper end being supported laterally by a ball bearing, con- 
struction of which is shown in detail in Plate 3, Brush 
holders and brushes 17 are shown in Plate 2. 

Plate 3; Figure 191. 

The details of upper bearing 3, Plate 2, are shown in Plate 
3, in which 4 and 5 are,, respectively, an exterior and interior 
ball race, separated by steel balls 6, part 5, the interior race 
being clamped rigidly to shaft 9, by means of nut 2. Part 
4 is stationary and sets in a recess in the main frame casting, 
the whole being covered by cap 1. Part 7 consists of a 
casting which is clamped between interior ball race 5, and the 
shoulder, pf shaft 9, so that it must revolve with the shaft 
at armature speed. This part (7) extends down 1 into oil 
well 10. The oiling action is as follows: Oil well 10 is filled 
with oil up tp approximately one-quarter inch of the top 
of the passage containing plug 13. Part 7 revolves at high 
speed, and, by the centrifugal action thus created the oil is 
forced up through passage 3-3, whence by gravity it returns 
again to the well through the bearing, thus flooding balls 
6 with a continuous stream of oil. 

Thirteen, Plates !- 2 and 3, is a plug closing the passage 


through which oil well 10 is filled. It is essential that this plug 
be in place and screwed tightly home, else the centrifugal action 
before named will force the oil out and empty the zvell. Plug 
12, Plates 1, 2 and 3; is for the purpose of draining oil well 
10, and this should be done at regular intervals every thirty days. 
After draining the oil well, insert plug 12 and fill the well 
with kerosense, start the machine and let it run for say two 
minutes, after which drain all the kerosense out, replace 
plug 12 and fill the well up to within one-quarter inch of the 
top of the passage stopped by plug 13. 

As the quality of oil to be used, see General Instruction 
No. 3, but: 

Caution. Never, under any circumstances, use the much 
advertised patent oils, as they almost without exception are 
worthless for the lubrication of heavy or high speed machinery. 
The use of such oils will invalidate the manufacturer's guarantee. 

On the other, or lower end of the armature shaft, is ball 
bearing 6, Plate 2, lubrication for which is furnished by grease 
cup 21, Plates 1 and 2. This grease cup should be kept filled 
with Alco Grease. 

Caution. It is important that either Alco Grease or a high 
grade vaseline be used, because of the fact that if a grease 
containing any acid is used in cup 21, the acid will attack the 
steel balls, and in course of time destroy their accuracy, thus 
compelling an unnecessary and somewhat expensive renewal of 
the bearing. 

Armature. The armature or revolving member of the ma- 
chine is completely assembled into one solid part, 1 to 6, 
Plate 2, in which 3 is the upper and 6 the lower bearing. 
The alternating current rotor, or revolving member, 4, is 
built up of reannealed electrical sheet steel, properly punched and 
assembled on armature shaft 9. The rotor bars are driven 
through the slots a tight fit, the ends electrically welded 
together into a solid mass of pure copper, which insures 
perfect contact, low resistance and a uniform torque, or 
pulling force. Directly above the rotor is fan 5, Plate 2, 
made of sheet steel blades and a solid ring, the blades 
riveted and welded together, and finally attached to shaft 9 
by means of two heavy set screws. This fan produces a 
suction through the ventilating openings in castings 18 and 
20, drawing cold air over the windings of the A. C. motor. 
This air is then forced up over this D. C. armature, and out 
through openings 23, Plate 1. 

Part 1, Plate 2, is the D. C. armature, which is mounted 
directly above fan 5. Armature coils are fixed in place with 



retaining band wires where the connections are made to com- 
mutator 2, Plate 2. The commutator is made up of hard drawn 
copper segments, insulated with mica, and held in place with steel 
rings clamped with four bolts. The D. C. generator is of the 
four-pole type, and is provided with commutating or inner poles. 

Brushes. The setting 
of the brushes is shown 
in Plate 4. There are 
four brush studs, 17, 
Plate 1, and two 
brushes to a stud. These 
brushes are attached to 
the holders by copper 
"pigtails." Particular 
care should be exercised 
to see that the screw 
holding the pigtail to 
the brush holder is kept 
set up tight, because 
unless the pigtail makes 
good contact with the 
holder, the tension 
spring will be com- Plate 4, Figure 192. 

pelled to carry current, 

which would probably heat the brush spring and destroy 
its temper. 

With regard to the amount of tension the brushes should 
have see General Instruction No. 8. 

The brushes are held in place by a curved arm pass- 
ing around the holder, ending in a tension ringer fitting on 
the top of the brush. The brushes are held to the commu- 
tator against the direction of rotation. The amount of tension 
can be adjusted by the spring and ratchet on the side of the 
brush holder. 

Care of Commutator. With regard to the care of the 
commutator, see General Instruction No. 8, 

The A. C. driving motor is the induction type, and is built 
either for single, two or three phase current, but the same 
machine will not operate on different phases. All standard 
machines are built to operate on both 110 and 220 volts. 

Installation. See General Instruction Nos. 1 and 2. 

The Rexolux is so built that it may be readily disassembled, 
since owing to its weight it would in many cases be difficult 
to hoist it in place in an operating room as a unit. In order 
to disassemble the machine, proceed as follows: 


First, open gratings 23, Plate 1, and remove the commu- 
tator brushes from their holders, allowing them to hang by 
their pig-tails so that you can make no mistake in getting them 
back into their proper holder. Remove screws 26, holding 
cap 14, Plate 1. Remove nut 2, Plate 3. Remove nuts 24, 
Plate 1 (four of them), holding main upper casting 7, and 
main lower casting 18 together. Screw the eye-bolts pro- 
vided into holes in main upper casting 7. (These holes were 
not in the first machines put out). Thrust pieces of gas 
pipe or steel bars through the eye-bolts and lift main casting 
7 straight up and off, laying it to one side, but right side 
up so that oil will not run out of oil well 10, Plate 3. Next 
carefully lift out the armature, first, however, having pro- 
vided two blocks or chairs, and lay the same down flatways on 
these blocks or chairs, so that the weight is entirely supported 
by the shaft. 

It is very important that you do not lay the armature 
down so that it rests on the side of the alternating current 
rotor 4, fan 5, or direct current armature 1, or commutator 
2, since any injury to these would be a very serious matter 
indeed. Handle the armature carefully and use a little horse 
sense, if you wish to avoid trouble. The machine may now 
be hoisted or carried into the operating room, where its 
reassembling will merely be a reversal of the process of 
disassembling. First carefully lower the armature into place, 
being careful that alternating current rotor 4, Plate 2, be on 
the lower end. Next replace casting 7, and tighten up nuts 
24, Plate 1, tight. Replace top ball races and nut 2, Plate 3, 
tightening nut 2 down as tight as you can get it. Replace 
cap 14 nd screws 26. Rotate the armature by hand to see 
that it turns freely, after which replace the brushes in their 
holders, put gratings 25, Plate 1, back into place, and the 
job is done. 

Be sure and wipe the inside of the top casting, clean, since 
if any oil should get on it, it would collect the copper dust 
from the commutator and might cause a ground on the brush 
yoke. See that the casting and brush yoke are thoroughly 
cleaned of all oil and dust before it is put back in place. 
It would be preferable to wash them with a cloth dipped in 
gasoline, wiping with a clean, dry cloth afterward. 

Bolts 29, Plate 1, hold pole piece 8, Plate 2, which carries 
coil 9, Plate 2, in place, and should not be removed under 
any circumstances, unless the coil be damaged and require 
rewinding. There are four of these pole pieces and eight 
bolts, two bolts per pole piece. Bolts 30, Plate 1, hold 



Direct/ or? of L.t 
ffofafion : 

/7/^>/?/ ft and /ook - 
//7g down or? ton . 

Plate 5, Figure 193. 


inner poles 10, Plate 2, in place, and should not be lemoved 
under any circumstances unless the coil is burned out and 
requires rewinding. 

Remember the switchboard sets directly over the machine, 
as shown in Plate 1. With each machine there is furnished 
four cork pads, 2 inches square by 1 inch thick, which are 
to be placed under the feet of the machine, where they act 
as a cushion, absorbing noise and vibration. It is not 
necessary nor do we recommend screwing the machine to 
the floor with lag bolts. Its weight is sufficient to hold it in 


In Plate 5, lines G-G show the direct current circuits. 
The current from the positive generator brush passes out at 
+ G, thence over the evenly dotted line to switch B (G, 
Plate 1), which when closed, connects, after passing through 
the ammeter, with the positive carbons of the arc lamp. 
From the negative brush of the generator the current passes 
through the various interpole coils in series, then out at G, 
thence similarly up to the negative side of switch B, and 
thence to the arc. In order to obtain the necessary field 
regulation, the extra lead from the shunt field is brought 
through the frame at F, Plate 5, and thence up to the field 
regulating resistance. The voltmeter is connected across 
the terminals of the arc at the right hand side of switch B. 
This completes the direct current connection for the type 
MA single arc Rexolux. 

Were it not necessary to obtain a self-starting motor, in 
single phase machines, it would then require but one set of 
windings. In order, however, to obtain the necessary start- 
ing torque, a second set of wire coils is superimposed upon 
the main power coils. This set of starting coils is thrown 
out of phase with the power coils by inserting in series 
therewith a starting resistance and reactance, shown opposite 
starting switch A, Plate 5. The main power coils terminate 
in the frame at "Ml" and "M2," Plate 5, and the terminals 
of the extra starting coil at T, the other end of which is 
connected inside of the machine to the main power coils. 
The lines designated by a dash and a dot constitute the 
alternating current wiring of the system. 

Where two or three phase current is supplied it is not 
necessary to use the extra starting coils, or the starting 




-p^. i ^ SS- 

L._.-L \jL/r?e 
jw[ * 1 

flBlll P p-^^ 

M -n-- 


1 ? 





resistance or the reactance. In this case the wiring incident 
to the starting features of the single phase motor is omitted. 


An examination of Plate 6 will show that the motor start- 
ing and control is identical with that shown in Plate 5, 
therefore what has already been said of Plate 5 applies. By 
reason of the fact that a shunt wound generator drops its 
voltage when overloaded, thus automatically protecting it- 
self when the carbons are brought together for the purpose 
of striking the arc, the shunt wound generator is ideal. Since, 
however, upon short circuiting the carbons the field of the 
machine . is entirely destroyed, it is impossible to run a 
shunt wound machine and keep one arc burning while the 
other is struck. During the period of changing from one 
projector to another to dissolve one picture into the next, 
it is necessary to operate the generator temporarily during the 
changeover interval, as a compound wound machine. The 
regulator shown above the center of the board accomplishes 
the changeover from shunt to compound wound during the 
time both arcs are burning, and then back to the shunt 
again when ready to extinguish one of the arcs. Regulator 
C accomplishes the whole changeover process without 
touching anything else. 

As in the previous description "+ G" and " G" are the 
main generator leads as they pass from positive and negative 
brushes respectively to the generator frame. In the two-arc ma- 
chine, however, the current passing from the negative brush first 
passes through the system of interpoles, thence through a 
separate series winding, wound on the main generator field 
poles. A tap is taken between the end of the interpole 
system and the beginning of the series winding and carried 
out through the frame at "S." The shunt field wire passes 
through the frame at "F" as heretofore. When, therefore, 
"+ G" and "S" are used as the main generator terminals, 
the machine is running as a shunt wound generator, similarly 
when "+ G" and " : G," it is running as a compound wound 

In the special regulator "C" the inner set of buttons and 
segmental contacts control one arc, similarly the outer set 
the other.. There are., two' similar regulator blades insulated 
from each other and moving together, one being elevated 
above the other. With the regulator blade in position No. 1, 


the generator is operating as a shunt wound machine with 
arc No. 2 shown open circuited. With the' regulator in posi- 
tion No. 1 and 2, circuit "S" for the generator is opened and 
connection " G" is used. The machine is therefore running 
as a compound wound machine. In passing over to position 
1 and 2 from arc 1 the arc No. 1 (controlled 'by the outer set 
of contacts) has also inserted with series therewith just 
enough ballast resistance to counteract the increased field 
strength due to cutting in the compound winding. 

This prevents a flicker on the screen which would otherwise 
ensue. Arc No. 2 (controlled by the inner set of contacts) 
has connected in series therewith its maximum resistance. 
This is sufficient to limit the short circuit current when the 
carbons of arc No. 2 are brought together to 15 amperes. 
By moving over to the two following buttons arc No. 1 
remains as it was at Nos. 1 and 2 and steps of resistance are 
cut on arc No. 2, thereby increasing the amperage to about 
35. The regulator is allowed to remain in this position until 
the carbons of arc No. 2 are well burned in, after which the 
regulator is quickly thrown to its final position No. 2. T,his 
extinguishes arc No. 1 and leaves arc No. 2 burning from a 
straight shunt wound generator. 

To pass back to arc No. 1 when the reel is completed on 
arc No. 2 the inverse order is followed, the explanation be- 
ing identical. In this type of machine the connections from 
the switchboard to arcs Nos. 1 and 2 are made from the 
studs shown and marked accordingly. The entire function 
of the regulator "C" in the two arc machine is to take ad- 
vantage of the perfection of both types of machine, shunt and 
compound, during the points in the transition at which they 
are of greater value. 


Figure 195 shows a general view of the Martin Rotary 
Converter, manufactured by the Northwestern Electric Com- 

According to literature which I have seen this device is 
made for 25, 30 and 60 cycle, 110, 220 or 240 volt supplies, 
delivering 60 to 80 amperes D. C. at the arc. Fig. 196 
shows the general construction of the machine. 

The manufacturers of this device were invited to supply 
proof of its electrical efficiency and cuts for its description in 
the Handbook, on the same terms accepted by other manufac- 



Figure 195. 

turers, viz: supply the cuts and 
assist in the preparation of the 
matter. They were invited to do 
this not once, but several times, 
and refused. Therefore beyond 
showing what it looks like, and 
,how it is constructed, I can only 
say that I have had both favorable 
and unfavorable reports as to this 
particular apparatus. From such 
information as I have had I believe 
the machine is well made mechan- 
ically, but that its electrical effi- 
ciency is rather low, due to the 
fact that it generates D. C. at 70 
volts and brakes down the sur- 
plus pressure with resistance. On 
the other hand its manufacturers 
claim, and I think their claim is 
well founded, that when their ma- 
chine is used one reel can be dis- 
solved into the other without in 
any way effecting the picture on 
the screen; also the resistance used 
to break down the surplus voltage 
makes the arc comparatively steady 
and easy to handle. 


Figure 196 


The Rotary Converter 


THE "Wagner White Light Converter" combines a 
motor and generator in one machine, having but one 
field and one armature winding. The motor action 
is that of a synchronous motor, which makes it necessary 
that the armature be brought up nearly to full speed before 
it can be run as a synchronous motor. The machine is 
built for single, two or three phase circuits, and for 25, SO 
and 60 cycle current, of any voltage from 110 to 550. The 
direct current voltage is 65 to 75, and the amperage capacity 
of the various sizes 35, 50, 70, 90 and 100 amperes. The 35 
ampere converter is intended for use in theatres where but 
one projection machine (one arc) is used. The 50 ampere 
size may be used in theaters having two projectors, provided 
the two arcs be not burned simultaneously for a period of 
more than two minutes. 

Plate 1, Figure 197. 

Plate 1 is a view of the Wagner single phase converter. 
Plate 2 is a view of the same machine disassembled to 
show the construction and parts. The mechanical con- 
struction of the single, two and three phase converters is 
practically identical, except as to the number of slip rings 
and brushes. 



By reference to Plate 2, the following parts are desig- 
nated by number: 2, A. C. or slip ring brushes; 3-3, end 
plates; 4, slip ring brush leads; 5, frame; 6 stator or field 

Plate 2, Figure 198. . 

windings; 7, armature shaft; 8, slip rings; 9, ventilating 
fans; 10, armature; 11, D. C. commutator; 12, ID. C. leads; 
13-13, main bearings; 14, D. C. brushes arid brush holders. 

The armature shaft, 7, P. 2, runs in bronze bearings 
13-13, P. 2, and underneath these bearings are oil cham- 
bers from whence a constant supply of oil is fed to the 
bearings by rings. See Fig. 179. These bearings are 
mounted in end plates, 3-3, P. 2, which are single-piece 
castings, bolted solidly to main frame 5, P. 2, thus insur- 
ing rigidity and freedom from vioration. The shaft pro- 
jects from the bearings at either end a sufficient distance 
to accommodate a pulley, so that when not generating 
direct current the converter may be used as a motor for 
driving light machinery, such as ventilating fans. It is not 
intended, however, that the converter be used to drive 
machinery and generate direct current at the same time. To 
attempt this might cause overload which would probably 
do serious injury to the armature windings. 

Once the converter has been started it requires no further 



attention, unless the power should for any reason be cut off 
for an appreciable period, in which case it will be necessary to 
restart the motor. 

Plates 3 and 4 are wiring diagrams of single phase con- 
verters, the only difference being dn the starting switqji. 
Single phase converters may be furnished with either three 

OnnectiOn Diagram 





Fuse and switch *i 
rto be for-nisKe-d by 

Before starting see that all 
switches are open. 
I. CLOSE switch 'I. 
ZTHROW-main switc .. 
starting position *2 and 
leave for approximately 
5 aeco-nels. 
d THROW -main switch to 

-running position *3. 
4 CLOSE switch <4-. If 

Connect J to S* 
Connect N to Ss 
If DC. volts are too low 
connect J to Si &. 

h; 9 her number. 
If DC volts are too h,qh 
connect J to Sz *. 
N to S- or r,e.t 

3W(tch *|, wait till converter 
stops, then open main A pole 

Connection Diagram for Single Phase Converter. 

Plate 3, Figure 199. 

and four pole starting switches, and both diagrams are, 
therefore, given here. Plate 5 shows the wiring of a two 
phase converter and Plate 6 of a three phase converter. 

Single phase converters are furnished with a single trans- 
former, while two and three phase converters are furnished 
with two transformers each. Wagner converters must take 
their A. C. supply through transformers, as they are wound 
to operate at a certain definite ratio between the A. C. supply 
and the D. C. delivery voltage, hence the voltage of the 
supply must be "stepped down" to that pressure which will 
cause the converter to deliver D. C. at the required voltage. 
This plan has one big advantage in that, should the voltage 
of the A. C. supply be altered at any time, as for instance 
from 110 to 220, 'the only part of the equipment it would be 
necessary to change would be the transformer or transformers. 

By examining the wiring diagrams and Plate 7 it will be 



noted that a number of connections may be made at the 
transformer by means of which one may raise or lower the 
A. C. supply voltage of the converter. These connections 
are marked SI, S2, S3, S4, S5, and S6 in the diagrams and on 
Plate 7. This arrangement gives an available range of vol- 
tage from 65 to 75 on the D. C. side of the converter, or 
allows one to maintain the voltage at any required point in 
case the alternating current supply voltage is variable. The 
wiring diagrams explain the method of using these taps. 

Connection Diorrn 

and switch '1 
ba furnished, by 


Before starting see that all 

Switches are, open. 
I CLOSE switch 'I 
2.THROW -main switch to 

Starting position 'Z and 

leave for approximately 

5 seconds 
3 THROW main switch to 

running position '3. 
4CL03E switch '<* If 

current is reversed, throw Note:- Select Size of corr, 9 - 

sw.tcK 4 to the other ponding to the leads to which 

pos.tion wire is to be Connected. 

S TO STOP converter, open 

switch- 'I, wait till converter 

stops then open-main 3 pole 


Connection Diagram for Single Phase Converter. 

Plate 4, Figure 200. 

. The Wagner converter may be used with any one of five 
different styles of resistance (rheostat) especially designed 
for this equipment, the same being designated as follows: 
Non-adjustable for single arc, Non-adjustable for multiple 
arc, Adjustable for single arc, Adjustable for multiple arc, 
and Duplex arc regulator. 

It is hardly necessary, I think, to enter into explanation of 
these resistances, with the exception of the "Duplex Regu- 
lator." This resistance is so connected that the moving of 
a single handle introduces by gradual steps the full value of 
the resistance into the circuit of one arc, at the same time 
reducing the resistance in the circuit of the other arc to a 



minimum, thus maintaining a uniform load on the converter 
during the process of fading one picture into another; i.e., 
changing from one projection machine to the other. 

The Wagner converter generates D. C. at from 65 to 75 
volts, hence it is necessary to use sufficient resistance to 
break down this voltage to that of the projection arc, which 
varies from 45 to 55. This resistance serves the purpose of 
a steadying ballast, making the arc steady and easy to handle. 



Connect J toS 2 (Trnformer0 
Connect K toS, OV.nsf ormer 
Connect L to S 2 (Transformer *2) 

Z.THROWmo.r, switch to runni. 

3 CLOSE sw.tch '3. If current , 

Not* Three 

3 pole leads m<tet bo connected 
to the main 3 pole: switch so A to qive clockwise 

t.rts ,n the wron, d.rect.on ch.nge over any two 
of the three (,. |.. d . , th . mm , n 3 pole .Jt ch . 

Connection Diagram for Two Phase Converter. 

Plate 5, Figure 201. 

Installation. Place the machine on a firm, level foundation, 
in a clean, light place, high enough from the floor so that it 
may readily be kept clean, and so that dust and litter cannot 
accumulate under it. Install the machine far enough from 
the wall so that it will be accessible from either end. See 
General Instruction Nos. 1 and 2. 

Wiring. The wiring from the converter to the control 
board (on starting switch) must be done according to local and 
underwriters' rules. A diagram of connections is sent with 
each converter, and is printed herewith, which diagram 
must be strictly followed. The connecting cables for an ordinary 
length of run should be at least as large as the corresponding 
converter leads. If the run is a long one the cables should be 


Oiling. A moderately heavy mineral bearing oil should 
be used, and the oil should be changed after each 200 hours 
of run. The oil level in the oil box should be kept about 
one-quarter inch below the lower part of the shaft. See 
General Instruction No. 3. 

Brushes and Care of Commutator. Before starting a new 
machine, examine end plate on commutator side and see 
that the small pointer fixed on the end plate is opposite the 
chisel mark on the rocker arm carrying the brushes. If it 
is not then move rocker arm until it is. 

Should the brushes begin to spark under normal load it 
will probably be found that the commutator has worn un- 
evenly and needs smoothening. Procure a sheet each of 
coarse and fine sandpaper, preferably garnet sandpaper. 
Do not under any circumstances use emery paper or emery cloth. 
(This stunt is recommended by the manufacturer, not me. 
Author.) Obtain a flat piece of wood about the same width 
as the commutator; place the coarse sandpaper around it 
and hold against the commutator when machine is running. 
Give the sandpaper just enough lateral (side) movement so 
that all parts of the commutator may be smoothed down 
evenly. When the rough places are all out, complete the 
smoothing process with fine sandpaper, using lighter pres- 
sure. See General Instruction No. 8. 

Fitting Brushes. When it is necessary to fit new brushes, 
proceed as follows : With the machine stationary, and the 
brushes fitted into the brush holders, a piece of coarse sandpaper 
is placed on the commutator, rough side toward the brushes, and 
grasping the sandpaper with one hand each side of the 
commutator, pull the sandpaper rapidly back and forth and 
the brush will be ground down and take the same curve of 
the commutator. See General Instruction No. 8. 

The brushes used on this machine are made especially for 
it, and are a mechanical mixture of metallic copper and carbon. 
When new brushes are required they should be purchased from 
the Wagner Electric Manufacturing Company. 

Starting a New Machine. After the installation and wir- 
ing has been completed, look well to the follwing points: 
(1) See that the A. C. line fuses, are in place. (2) See 
that the converter oil boxes are filled with oil. (3) See 
that the pointer on the end plate coincides with the chisel 
mark on the rocker arm carrying the brushes. Everything 
is now ready for starting up and the instructions which are 
sent out with each converter (and printed here) should be 
carefully studied. See that all switches are in the open position, 



then: (1) Close A. C. line switch. (2) Throw main four-pole 
switch (or three-pole as is the case) to starting position, and 
leave for approximately five seconds. (3) At end of five seconds 
throw main switch to running position. (4) Close polarity 
changing switch either way. (5) Bring the arc lamp carbons 
together, and quickly draw them apart to start the arc. 

On account of the peculiar characteristics of the converter the 
polarity of the .arc lamp may at times be reversed in starting, 
and it is therefore necessary that a polarity reversing switch be 

Before starting see that all switches 
are open. 
LtHROW main switch te start m, 

rition^l and leave for approximately 
2.THROW main awit ch te runnine, 

position 2. 

3. CLOSE switch *3.If current is 
reversed, throw switch *3 to the other 

4.TO STOP, converter open main* rl 
switch. ' . 

Motet L.t*'.tjgtd9 must be connected 
to the mmin/A pole switch so as to give 
(from correlator end) direction of rotation;^ maehiM 
starts in the wrong direction change over 
line leadj of one phase on the rnain 4 pole switch. 


Connect J to S| (Transformer^) . 
Connect K t.S, frnjn,f.mre <*Z) 
ConnertL toS z CTrensforiner'2l 
If D.C. volts are too low, connect K to lesds of 
transformers 1*^,and leads J -Lto Sj or S,. 

If D.C. volts are too hio,h,connect Kto leads Si of 
transformers*! *x-*fe,a.nd. iuts J , L to St or S t . 



omWred leads. eeen n its cvn trMfrmer.Th 

oth to S,, both to St, or both to Sj. 

Note.- Select size f ,r. corretpondinj to the 

which wtre ito be connected 

Connection Diagram for Three Phase Converter. 

Plate 6, Figure 202. 

included between the D. C. resistance and the arc. This 
switch is shown in Plate 4. After starting the converter and arc, 
if it is found that the polarity is reversed and the crater is 
forming on the negative carbon, the polarity switch should 
be thrown over. (6) To stop converter open switch 1, wait 
until the converter stops, and then open main four-pole switch. 
It sometimes happens that trouble is experienced in start- 
ing the converter for the first time. The most common 
sources of trouble are: Converter will not start after clos- 
ing A. C. line and throwing three or four pole switch to 
starting position. This may be caused by any one or more 
of the following things: (a) A. C. line fuses either not in 
place or faulty, (b) Switch contacts not making good con- 



tact with the switch jaws, (c) Brushes lifted off commu- 
tator, (d) Mistakes in connecting up. 

If no trouble is experienced in getting the converter started 
it sometimes happens that the fuses blow upon throwing the 
four-pole switch over into starting position. This may be 
caused by switching over before the motor has attained its 
full speed. Until the operator gets experience in estimating 
the correct motor speed it is advisable for him to time himself. 
On the other hand, too long an interval must not be allowed or 
the converter will pass the synchronous speed. It is ex- 
pected that five seconds will bring the armature up to proper 
synchronous speed. 

Plate 7, Figure 203. 

If the converter stops after switching into running posi- 
tion 3, examine the slip ring brushes, also the transformer 
connections, and see that the switch blade and jaws are 
making good contact. If a vicious sparking is seen on the 
commutator it indicates a break in some of the connections 
running to ' leads A, B, C, D, Plates 3, 4, 5 and 6. This 
trouble can be readily recognized if a polarized D. C. volt- 
meter is connected across leads G and H. It is evidenced 
by a periodic swing, forward and back, of the voltmeter 
needle. If there is continuous sparking, the switch contacts 


and blades connecting to converter leads E and F should 
be examined and any faulty contact made good. If this does 
not remedy matters the trouble may be due to commutator 
being rough, though this is not a trouble to look for in a 
new machine. It has been assumed that the operator has 
made sure that the pointer on the end plate is opposite the 
chisel mark on the rocker arm, as sometimes the rocker 
arm gets displaced during shipment, and such displacement 
will cause sparking. 

Hallberg's D. C. to D. C. Economizer 

THE Hallberg D. C. to D. C. Economizer consists es- 
sentially of a D. C. motor which pulls a specially 
wound generator delivering current to the arc at arc 
voltage, without any resistance in series. The only waste is, 
therefore, that consumed in the machine itself. In other 
words it costs more than the rheostat, but saves the dif- 
ference between its efficiency and the efficiency of the rheo- 
stat. This is very great on voltage of 220 or more, and is 
considerable on 110. The manufacturer claims the following: 


, Line Input , , Output at Arc 

Line Line 

Fuses Line Am- Line Arc Arc Arc Watts Em- 
Required. Volts, peres. Watts. Voltage. Amperes. Watts. Loss, ciency. 

20A 110 17 1,870 50-55 30 1,650 220 88% 

10A 220 10 2,200 50-55 30-35 1,650 550 75% 

5A 550 4 2,200 50-55 30-35 1,650 550 75% 

The table or data is explicit, and if the manufacturer will 
base the payment of his bill upon the accuracy of the figures 
given the machine ought to prove a good investment even 
for 110 volt current, since the control of D. C. through a 
rheostat is, as we all know, enormously wasteful. A rheostat 
has considerably less than 50 per cent, efficiency. 

Fig. 204 illustrates the general make-up of the 110 volt type of 
economizer, which, while being constructed along the lines of a 
motor generator, is in the strict sense of the word only in part 
a motor generator. The principle involved is original with Mr. 
Hallberg and permits the use of a smaller and more efficient 
motor and generator than would be possible were the apparatus 
a straight motor generator set. The 110 volt outfit is provided 
with an automatic starting box and light controller by means 
of which the operator can vary the amperes at the arc anywhere 



from 20 to 30, on the 25 ampere size ; from 30 to 40 amperes on 
the 35 ampere size, and from 40 to 60 on the 50 ampere size. It 
is,' of course, possible to secure lower ampere output than speci- 
fied as a minimum with any of the above machines by the use 
of special controllers, which can be furnished upon request. 
Fig. 205 illustrates the Hallberg D. C. economizer as made for 
voltages ranging from 200 to 750. This outfit is a straight motor 

LINE ruses 
15AM PS. row I (0 VOL.T& 
10 220 
5 - 550 




Figure 204. 

generator set, in which, however, the generator is of special con- 
struction delivering a steady ampere flow to the arc without the 
use of a rheostat. The 200 to 750 volt outfit is also furnished 
complete with automatic starter and light controller, and be- 
sides this outfit has a pully coupling between the motor and gen- 
erator on which, in special cases, a belt may be placed for driving 
the economizer by means of an engine, which would make the 
economizer operate a motion picture arc just as it does when 
driven from an electric circuit, and at the same time from the 
high voltage side current can be taken for driving fan motors, 
or a limited number of lamps. This is an important feature and 
might, under some circumstances, be of considerable value to an 

Another feature of construction is that the low voltage side of 
the economizer is a separate unit which can be run as an ordinary 
dynamo by an engine ranging from 3 to 6 horsepower in capacity 


for the operation of a motion picture arc. The other half of the 
machine, representing the high voltage side, is an ordinary elec- 
tric motor which can be taken off its base in a few minutes' time 
and used as a regular electric motor, together with its automatic 
starter. These are points of economy which represent certain 
advantages to the purchaser of this class of apparatus. It is not 
practical to give wiring diagrams, showing the connections for 
these machines, because they vary for different voltages and cur- 

Figure 205. 

rents, and as these machines are generally built to specifications 
to suit the individual operator or manager, it is best to depend 
upon the blue print and diagram of connections which accompany 
the shipment, and if the instructions should be lost, another set 
can be readily obtained at the office of the manufacturer. 


1. Installation. (See General Instruction Nos. 1 and 2.) 

2. Connections. All connection should be made as shown 
in the wiring diagram sent with each machine. They must 
be clean and tight. Fuses should not have a higher capacity 
than that indicated by the diagram. 

3. Brush Tension. After the machine has been properly 
set and connected, rotate the armature by hand and examine 
each and every carbon brush to make sure that it moves freely, 
without the slightest friction in the brushholder which guides it. 
Make sure that the flexible copper cable, or pigtail, as it is 
called, is properly clamped by the screw in the brushholder cast- 
ing provided for that purpose. When the brush is in proper con- 
dition and moves freely in the holder, the next point to be 
looked after is the spring tension which pushes the brush against 
the commutator. See General Instruction No. 8. The 


brush tension spring is adjustable by putting the end of it in the 
different notches provided for it in the brushholder casting, and 
any degree of tension can be had by using the different notches. 

4. Oiling. The oil chambers should contain enough oil to 
give the rings a good dip. The oil level will be seen in the gauge 
on the sides of the bearings and should be merely at the top of 
the gauge. When starting the machine, lift oil chamber covers 
and see that the oil rings are turning freely and carrying oil to 
the shaft. The old oil should be drawn off by unscrewing the 
drainage plug at bottom of the bearing every month or two, and 
replaced with new oil. See General Instruction No. 3. 

5. Setting of Brushes. Machines are shipped from the 
factory with the brushholders and brushes properly set. The 
position of the brushes is approximately half way between the 
poles. In the motor, they are placed one or two segments back 
(that is, against the direction of rotation) of the exact middle or 
neutral point, while in the generator .they are set one or two seg- 
ments forward. The brushholders should be placed on the studs, 
so that the brushes will not run in the same line on the commu- 
tator. This will help to avoid grooving. 

6. Starting Set. First see that the starting box lever 
has moved back to the off position. If there is a regulating rheo- 
stat on the motor end, its handle should be moved as far as possi- 
ble in a contra clockwise direction. If there is one on the gen- 
erator end, its handle should be moved as far as possible in a 
contra clockwise direction. Close the main switch and move the 
lever of the starting box over the contacts, taking about one sec- 
ond for each, until it is against the magnet which will hold it. 
If the set has not started when the fourth contact point is 
reached, open the main switch and ascertain the trouble. When 
the set is running, the current may be adjusted by means of 
the regulating rheostats. 

7. Stopping Set. Open the main switch and let the start- 
ing box operate itself. The lever will be released when the 
motor has slowed down, when it will fly back to the "off" posi- 
tion. If the contacts become rough and prevent the lever from 
moving fully back, they should be cleaned with very fine sand- 
paper. The lever should never be fastened or allowed to stick 
at an intermediate point. 

8. Care of Brushes and Commutator. (See General In- 
struction No. 8.) 


Hallberg's Twentieth Century Motor- 
Generator Set 

JH. HALLBERG, New York, has put out a motor gen- 
9 erator set, the general design of which is shown in 
Plate 1, Fig. 206. The machine occupies a floor space 
15 by 31 inches, and is 15 inches in height. Its weight is 
a little less than 500 pounds in the 70 ampere size, the 40 and 
130 ampere machines being respectively less and greater in 
weight. The machine is compact, rigid in construction, and 
its parts are easily accessible for adjustment or repair, as is 
made evident through an examination of the various plates. 
The machine is made in capacities of 20-40 amperes, 30-70 
amperes, and 60-130 amperes. The 30-70 ampere size is 
the capacity more largely in demand for moving picture 

Plate 1, Figure 206. 

work, in that it will operate with a fair degree of efficiency 
on a 30 ampere load, and will carry two 50 ampere arcs for 
the short period of time necessary to make a change from 
one machine to the other. It must not be understood from 
this that the generator will stand up under a 100-ampere load 
for more than one to one and a half minutes. 

The machine delivers direct current to the arc, at arc 
voltage, without any resistance interposed in the circuit, 
which means, of course, that it is a specially compounded 
generator, and, to go a little further, a specially compound- 


ed generator pulled by an A. C. motor, the two armatures 
being mounted on one shaft, and contained in one housing, 
with a ball bearing at either end of the shaft, both being "ball 

Plate 1 supplies a view of the whole machine, with the 
various parts numbered. 

No. 1. Lubrication. The lubrication of this machine dif- 
fers from that of most other motor-generator sets used for 
moving picture work, in that grease is used instead of oil. 

The grease chambers may be filled in two ways: first, if 
you have purchased your grease in a "gun," or if you have 
a "gun" which can be filled with grease, having removed 
screw, 23, Plate 1, and a similar one on the opposite diameter 
of the grease chamber cover, you can place the spout of 
the gun in the upper hole and force grease in. This will 
force the old grease out at the lower hole, and the job will 
be a fairly complete one. This operation must be performed 
for the grease chamber at each end of the armature shaft. 
When through you will, of course, replace the screws. 

Another way is, if you have no grease gun, to remove 
screws 24 (four of them), on the end of the cast iron cap 
which covers the grease chamber. You can then pull the 
cap off, clean out the old grease, and pack the chamber with 
fresh lubricant. Where this is done it would be well to 
wash out the grease chamber thoroughly with kerosene or 

Still a third way is to remove screw, No. 23, Plate 1, and 
insert in lieu thereof a compression grease cup having a stem 
of the same diameter and thread as a one-eighth inch gas 
pipe. Where the compression grease cup is used when it is 
desired to force grease in it will be necessary first to remove 
the screw in the opposite diameter to screw 23, Plate 1, 
same being immediately below the grease cup, in order to 
allow an equal amount of old grease to flow out. Where the 
compression grease cup is used it is merely designed that 
the cup take the place of a grease gun therefore it should 
be a large one and only used to force a large quantity of 
grease in about once every 60 to 90 days, it being expected 
that when the run is, say, twelve to fourteen hours per day 
one greasing will last for that length of time. 

Caution: Don't use any and every kind of grease. The 
grease serves ball bearings, and if it contain alkalis or acids 
you may expect trouble and plenty of it. For this reason my 
advice is : Use only grease procured from the manufacturer 
of the machine. You may regret it if you do otherwise. 


No. 2. Locating the Motor Generator. (See General In- 
struction No. 1.) 

No. 3. Installation. (See General Instruction No. 2.) 

No 4. Cleanliness. (See General Instruction No. 4.) 

No. 5. Loose Connections. (See General Instruction No. 

No. 6. Ammeter and Voltmeter. (See General Instruc- 
tion No. 7.) 

No. 7. Removing End Bearing Bracket 2, P. 1. It will 
never be necessary to remove this bracket unless some fault 
should develop through the use of improper grease, or a 
very improbable inherent imperfection in the ball bearings, 
but should such a thing occur you may remove end bearing 
bracket 2, P. 1, by first removing four hexagon shaped nuts, 
holding the cast iron cover of the grease chamber. These nuts 
do not show in the plates, but correspond to nuts 24, P. 1, in the 
grease chamber cover at the opposite end of the machine. The 
studs, which are held by four hexagon nuts, not only 
hold the outside cast iron cover to the grease chamber, but 
extend through and into an inside cast iron grease chamber 
cover. The ball bearings are clamped between these two 
end covers, and these bearings should never be removed 
from the armature shaft except it be desired to install a new 
bearing. Therefore, after having removed the hexagon nuts 
and the outside cover, using a copper punch and hammer, 
gently drive the studs inward to loosen the inside cover. 
Having done this, remove bolts 4, P. 1 (four of them), where- 
upon you may pull away end bearing bracket 2, P. 1. 

No. 8. To Remove the Ball Bearing at the A. C. end of 
the armature, follow Instruction No. 7. Having done so you will 
see on the end of the shaft a nut having in its edge a saw 
kerf, and in its face the head of a machine screw. This 
screw acts as a lock nut by compressing the edges of the 
nut where the saw kerf is made, thus locking the threads to 
the shaft. Loosen it and remove the nut, which has a right- 
hand thread. This will release the ball bearing, which may 
be pulled out. When installing the new ball bearing or re- 
placing the old one, be sure and get it on the shaft straight or 
"square." If you attempt to put it on a slant it won't go, 
but if started on just right will slip on easily. Having it in 
place, set up the lock nut as tight as you can get it, and then 
set up the screw in its face, thus locking the nut to the shaft. 
In replacing end bearing bracket 2, P. 1, proceed carefully, 
and don't try to force it on over the ball bearing. When you 
get it exactly right it will slip on without any trouble what- 



ever. If it does not do so, that is your fault and not the 
fault of the bracket you have not got it exactly in the right 
position with relation to the bearing. If you try to force it 
on you will probably succeed in ruining the ball bearing. 
The rest of the process of replacing is simply the reversal 
of the process of disassembling. 

No. 9. To Remove the Armature lift out all the brushes, 
17, P. 2. To do this lift finger 9, 'P. 3, and pull the brush 

out, letting it hang by its 
pig tail so that you will be 
sure to get it back in the 
right holder. Next remove 
bolts 4, P. 1 (four of them). 
Next remove the four hexa- 
gon-headed bolts, 24, P. 1, 
holding grease cover cap, 
22, P. 1, and pull the arma- 
ture, carrying end bracket, 
2, P. 1, with it, straight out 
at the A. C. end. 

Caution: Never lay an 
armature dozvn flat on any- 
thing. Either stand it on end, 
or else support it on two 
chairs or boxes, using the 
ends of its shaft for the 
purpose. If you lay the 
armature itself down on the 

floor or table you are likely to injure the insulation. The 
replacement of the armature is simply a reversal of the proc- 
ess of taking it out, doing each step in its turn. 

No. 10. To Remove the Commutator End Bearing Bracket, 
3, P. 1, first remove four hexagon headed bolts 24, P. 1, in 
grease cover cap, 22, P. 1. Next lift out all the brushes. 
They may be lifted out by raising finger 9, P. 3. Let them 
hang by their pig tails, so that you will get them back in the 
right holder. Remove bolts 4, P. 1 (four of them), where- 
upon the bracket may be pulled away. 

Caution: The four hexagon head bolts extend through 
and hold the plate covering the inside end of the grease 
chamber. This cover will sometimes stick slightly. Before 
removing the bolts, but after having backed them out for 
three or four turns, tap on them lightly with a hammer, in 
order to loosen the inside grease chamber cover. 

Plate 2, Figure 207. 



No. 11. To Remove Brush Yoke, 6, P. 2, follow Instruc- 
tion No. 10, then loosen screw, 7, P. 2, whereupon you may 
pull away the yoke, carrying all the brush holders. 

No. 12. Brush Holder Stud. Should it ever be necessary 
to remove brush holder stud, 8, P. 2, it may be done by 
loosening nut, 10, P. 2, but if you do this, be very careful in 
reassembling that the insulation, which consists of two mica 
washers, 9, P. 2, and a mica sleeve around the bolt, be not 
in any way injured. If this insulation is not perfect, then 
the whole frame of the machine will be charged with po- 
tential. In loosening these parts it will be well to remove 
nut 10, P. 2, and thoroughly clean the contact between it and 
the copper clip to which the wire is connected. In reassem- 
bling be sure to set up nut 10, tight, else you will not have good 
electrical contact; also it is essential that the lock nut be- 
hind nut 10, which holds the insulation in place, be set up 
tight, else the brushholder stud will vibrate and thus cause 

No. 13. Brushholder, 12, P. 2, may be slipped off at any 
time by loosening screw 16, P. 2. Before taking off the 
brushholder you should make a scratch mark at its end on 
the stud, so that in re-f 
assembling you may 
get it back in exactly 
the same position it 
formerly occupied. 

No. 14. Care of the 
Commutator. (See Gen- 
eral Instruction No. 8.) 

No. 15. To Install 
New Brushes. First raise 
finger 16, P. 1 (shown 
better at 9, P. 3), and 
remove the screw hold- 
ing the end of the pig 
tail to the brass cast- 
ing, then lift out the 
brush, put in the new 
one and attach its pig 
tail to the casting the 

same as the old one was. Plate 3, Figure 208. 

The face of the new brush 

must be ground fitted to the curve of the commutator. To do this 
lift out all the brushes you are not replacing, then place on 
the commutator, sand side out, a strip of No. 1 sandpaper 



long enough to extend one and one-half times around its 
circumference. Lower the new brush on this sandpaper 
under the pressure of its tension spring, and revolve the 

armature until the 
brush is ground down 
to a proper bearing. It 
is also possible to lay a 
piece of sandpaper on 
the commutator and 
pull it back and forth, 
but the other way is 
the better. 

No. 16. Heating- (See 
General Instruction No. 


No- 17. General Re- 
marks. Plate 3 shows 
the construction of the 
brushholder in detail, 
14 being the pig tail, 11 
the spring which gov- 
erns the amount of 
tension supplied ihe 
brushes through finger 
9, P. 3. Plate 4 shows 
the pole piece con- 
struction, main poles AA being wound and BB not wound. 
In like manner interpoles or "commutating poles" C, are 
wound, while DD shows the core of the poles without 
the windings. The machine is entirely self-contained, and 
requires no special base. It may either be set on a cement 
floor and bolted down or on any other reasonably solid 
foundation, but if installed in the operating room it should 
be set on a felt pad, as per General Instruction No. 2. This 
will take up all vibration, make the machine practically 
noiseless, and there will be no necessity for bolting it down 
at all. 

The efficiency of the machine is claimed by the manufac- 
turer to be between 65 and 70 per cent, depending upon 
local conditions and the degree of intelligent care given. 

The accompanying connection diagrams are quite plain, 
and may, I believe, be followed without any trouble by the 
average well-posted operator. Plate 5 shows the various 
connections for single, two and three phase 110 or 220 volt 

Plate 4, Figure 209. 



All Hallberg Twentieth Century A. C. to D. C. motor genera- 
tors are so wound that they may be used either for 110 or 220 
volt current, merely by changing the connections as shown in P. 5. 

Two-Arc Machine. P. 6 shows the wiring of the D. C. 
end, with two projection arcs connected in multiple with 
each other. By this arrangement arc No. 1 may be operat- 
ed at any desired amperage between 30 and 60 by moving 
the handle of the field controller, which has twenty-one 


J 1 

Plate 5, Figure 210. 

contacts, supplying twenty-one different current values. When it 
is desired to start the second arc and fade the first picture 
into the next, the operating or machine switch on machine 
No. 2 may be closed, and when the time comes to swing 
over to that machine its arc is started merely by bringing 
the carbons together and separating them in the usual man- 
ner, which will automatically extinguish the arc of machine 
No. 1, thus fading one picture into the next. This is a matter 
which will require some practice, but once it is mastered it is 
quite possible to secure fair results. But where this plan is 
used the operator will do well to burn craters on his carbons 
when there is no picture on the screen. In other words, ht 
should have a supply of burned-in carbons. It will prob- 



ably also be found necessary to recenter the upper crater 
by raising the lamp about one-quarter of an inch before 
starting the arc. The machine motor must, of course, be 
started at the same time the arcs are changed over. The man- 
ufacturer claims that one of the peculiarities of this genera- 
tor is that it picks up and steadies its arc almost instantly. 

P. 7 shows the machine connected to a single-phase cir- 
cuit, with an emergency circuit of two economizers which 

may be put into service 
merely by throwing 
over the upper three- 
pole switch. P. 7 also 
shows a switchboard 
upon' which is mounted 
the controller shown in 
P. 6, by means of 
which the amperage at 
the arc may be varied 
at the will of the oper- 
ator, or, When two arcs 
are* to be operated at 
the same time this con- 
troller is used to secure 
the desired D. C. am- 
perage within the ca- 
pacity of the machine. 
The lower three-pole, 
double-throw switch in 
P. 7 is so connected that 
when the handle is to 
the right, the compound 
winding on the gener- 
Plate 6, Figure 211. ator opposes the shunt, 

which causes the gen- 
erator to produce constant current for the operation of one 
arc at a time, in which case no resistance is necessary in 
series with the arc, the generator having within itself the 
necessary flexibility to properly control the arc. 

Examining this switch you will notice that when it is 
to the right its lower blade short circuits the resistance im- 
mediately below it. This resistance is in two units, the same 
being in multiple with each other, and the negative arma- 
ture wire from the generator is connected to its center. By 
this arrangement the current going through either one of 
the arcs enters the outside terminals of the resis'tance units 



and travels through them back to the negative pole of the 
generator. This resistance offers a drop of about 5 volts 
when the two resistances are in parallel with each other and 
in series with the arc, and it is in some instances found 

//O VOLT off 

Plate 7, Figure 212. 

desirable to leave the resistance in circuit. For highest 
efficiency, however, there can be furnished an extra switch 
blade, by means of which the resistance unit can be entirely 
short circuited when the three-pole switch is to the right 
for single lamp operation. When the lower three-pole switch 


is to the left the compound windings on the generator are 
reversed and act with the shunt field, which makes the 
generator a cumulative compound machine, under which con- 
dition it produces constant potential. When the lower three- 
pole switch is to the left the short circuit across the resis- 
tance unit is open and the resistance is now connected so 
that the left-hand half is in series with one of the arcs and 
the right-hand in series with the other arc. The upper three- 
pole, double-throw switch is to the right when the generator 
is working, but should the generator break down it is only 
necessary to throw it over to the left to cut in alternating 
current at the arc through the economizers. 

A-A, P. 7, Fig. 212, are ammeters, one for each arc, and V 
the voltmeter. At the top on P. 7, it will be observed that 
arc No. 2 takes current through a double-pole, double-throw 
switch. This arrangement is offered as a suggestion where 
in some instances it is necessary to take extra precaution in 
order always, under all conditions, to maintain one of the 
arcs. For instance, in some theatres where the entire pro- 
jection installation is supplied from the electric company's 
two or three phase service the house lighting may be on an 
entirely separate set of mains, with separate transformer 
and meter on single phase. The house lighting system may 
be fed from another street, one or more blocks away. In a 
case of this kind the second emergency connection from the 
single phase or house lighting service may be brought into 
one of the machine switches through suitable means of vol- 
tage reduction, by the use of one of the sets of terminals on 
the double-throw, double-pole switch. In P. 7, the lower 
three-pole, double-throw switch is to the right for one lamp, 
and to the left when two lamps are being operated. 

Mercury Arc Rectifier 

General Remarks 

THE mercury arc rectifier is a device marketed by two 
manufacturers, the General Electric Company and the 
Westinghouse Electric and Manufacturing Company, 
for the purpose of changing alternating current of standard 
line voltage to direct current at arc voltage, the reduction in 
pressure being accomplished by means' of an auto transformer 
which is an integral part of the machine. 

In describing the "Principle of Operation," let it be clearly 
understood that I have sacrificed accurate correctness in 


favor of "understandableness." To tell exactly what happens 
inside of a rectifier tube would be a good deal like trying to 
explain what electricity is or to explain the reason for the 
force of gravity. Electrical engineers acquainted with the 
mercury arc rectifier have various opinions as to exactly 
what takes place inside the tube, and while I have every 
respect for the opinion of these eminent gentlemen I am ad- 
vancing a theory which, while it may be entirely wrong, 
sounds to me like common sense. In fact I wrote it with 
two ends in view, viz.: first, to make the matter understand- 
able to the ordinary operator; second, to set forth my view 
of what ought to take place, simply viewing the matter in 
the light of common sense. With this explanation the fol- 
lowing is submitted: 

Principle of Operation. The mercury arc rectifier consists 
essentially of a sealed- glass bulb, from which the air has 

Figure 213. 

been exhausted, provided with four terminals, A, Al, B and C, 
Fig. 213. Within this tube is a quantity of mercury the 
purpose of which will be explained further on. The two 
upper terminals A, Al, Fig. 213, are of graphite or other 
suitable material, and the two lower ones B, C, Fig. 213, 
are of mercury, the smaller one of the two, C, Fig. 213, being 


what is known as a "starting terminal." When the bulb is in 
a vertical position the', pools of mercury in terminals B and C 
are separated, but when the tube is tilted or rocked sidewise 
(to the left) these mercury pools are brought temporarily into 
contact with each other for the purpose of starting the tube 
into action. 

The vacuum bulb, in its active state, contains vapor of 
mercury, which is a conductor of electricity only under cer- 
tain conditions. Current will readily pass from either one 
of the graphite terminals, A, Al, Fig. 213, into the mercury 
vapor, and, with the circuit completed by the arc, will pass 
from it into mercury terminal B, and thus on through the 

Alternating current, however, changes its direction many 
times in the course of a second of time, but when the direc- 
tion of flow seeks to reverse itself and pass from the mercury 
to the graphite terminals, these terminals offer resistance 
which prevents the flow, and thus the graphite terminals 
act as check valves, permitting the current to pass into mercury 
vapor, but preventing it from passing into the graphite terminals. 

The alternating current supply circuit is connected to 
graphite terminals A, Al, Fig. 213, through an auto-trans- 
former which lowers the voltage to that required at the arc, 
and as the action is such as will only allow current to flow 
in one direction, the pulsations of current which pass alter- 
nately/ from terminal A and Al, Fig. 213, into 'the mercury 
vapor must, of necessity, pass out of the vapor through 
mercury terminal B, Fig. 213, which is connected to the 
arc lamp, and thus we have a continuous, slightly pulsating 
current delivered at the arc. The pulsations would ordinarily 
be quite pronounced on the D. C. side, but this matter is 
taken care of by a feature of the auto-transformer (an 
integral part of the machine) which serves to "flatten out" 
or decrease the natural pulsations, so that the current deliv- 
ered at the arc has a very nearly constant potential value. 

Before the bulb starts 1 to rectify, the mercury vapor is 
absent, and, between electrodes A, Al, B, and C there is a 
vacuum which presents high resistance, and this space must 
be filled with mercury vapor before current can pass. Once 
this has been accomplished, however, and current flow has 
started, it will continue to flow as long as the supply is 
uninterrupted. Any interruption of the supply, however, 
even for the shortest period of time, permits the vacuum 
to re-establish itself and stops the operation of the bulb. 


In order to establish the mercury vapor, or conducting 
medium, the bulb is tilted so that the space between the 
large and small mercury pools in terminals B, C, is tem- 
porarily bridged by mercury, whereupon current passes be- 
tween terminals B and C through a special circuit provided, 
directly from the A. C. supply lines. As the tube rocks back to 
upright position this little mercury bridge between terminals 
B and C is broken, and in breaking it forms an arc or spark, 
and it is this arc or spark which creates the initial current 
carrying mercury vapor and puts the tube into operation. 
Once operation is started the rectifier will continue to operate 
indefinitely as long as the current supply is uninterrupted. 

The alternating current supply c : rcuit is connected to an 
auto-transformer 1 or main reactance, the terminals of which 
are connected to the terminals A, Al, Fig. 213. From ter- 
minal B the current passes through the arc and the circuit 
is completed through a connection to the middle point of 
the auto-transformer. 

In the main, rectifiers consist of: (A) an auto-transformer; 
(B) a regulating reactance coil; (C) a tilting mechanism; 
(D) a relay; (E) a dial switch; (F) a switch or other means 
for connecting the auto-transformer directly to the arc, and, 
(G) a bulb and its holder. 

The reactance coil is for the purpose of giving steadiness 
to the arc and limiting the current when the carbons are 
brought together when striking an arc (a dead short circuit) 
to a value which will not be injurious to the bulb. 

Modern rectifiers are so equipped that in case the bulb gives 
out the operator can swatch over to the auto-transformer and 
continue the show with alternating current, using the auto- 
transformer as an economizer. Also modern rectifiers are 
equipped with a dial switch by means of which the operator 
can instantly vary the amperage within certain limits. 

Installation. Rectifiers are ordinarily received in two 
separate shipments, one of which, the rectifier itself, weighing 
several hundred pounds, will probably come by freight. The 
other, the glass bulb, is carefully packed in a specially made 
case, and is usually sent by express. In removing the bulb 
from its crate proceed strictly according to directions in 
loosening the crate, after which carefully lift out the bulb. 
It will be in an inverted position. Turn it slowly over and 
carefully let the mercury run down into terminals B, C. In 
rolling the mercury should make a sharp, cracking sound, 
which is an indication that the tube is in good condition. 


The rectifier should not be located directly in the operat- 
ing room unless there be some means provided for covering 
the bulb so that its light will not shine in the room. Light 
in the operating room is highly objectionable. One very 
good method is to install the rectifier in an adjoining room 
and cut a space through the wall just large enough to admit 
the front panel of the rectifier. This allows the operator to 
have access to the switches for the purpose of varying the 
amperage, or changing over to A. C., and at the same time 
excluding the light from the room. 

Some managers place the rectifier in such position that it 
can be seen from the front of the theatre where the weird 
greenish light given off by the bulb attracts considerable 
attention. As a general proposition, however, the modern 
rectifier which allows of changing amperage by means of a 
switch should be so located that the operator can reach 
these switches without leaving the operating room. 

There is no vibration and no noise except a humming 
sound which emanates from the transformer. Care should 
be exercised that there is no sheet metal near the machine, 
sincei if there is the transformer would probably set up 
vibration therein and thus create more or less objectionable 

Comparative Results. Experiments made by Simon Henry 
Gage and Henry Phelps Gage, Cornell University, have 
shown that the losses through the pulsation of the current 
with the mercury arc rectifier are but very slight. A mer- 
cury arc rectifier using 40 amperes at 52 volts gave 12,150 
C. P., whereas straight D. C., 40 amperes at 51 volts, with 
the same carbon set only gave 12,350 C. P., a difference of 
about 200 C. P. 

Tubes should never, under any circumstances, be operated 
above their maximum capacity. 

On the following page appears a chart indicating the 
various troubles one is likely to encounter when operating 
a rectifier, together with the most probable cause or causes 
of each. A careful study of this diagram ought to be of 
much value to users of rectifiers. With this chart and fche de- 
tailed instructions contained in this book, plus a fair supply 
of "horse sense," I believe any operator ought to handle a 
rectifier without any serious difficulty. 



r> 3 

'* r 

/Current at switch Fuses blown. 


J \ No current 

at tube 


S 1 terminals. 


u ^ 

l.No current at switch Line voltage 




'Friction or bent stud. 





H 1 

Relay contact is poor. 


^ Relay contact not closed. j Tilting clrcuit open 





Secondary coil of magnet short- 


CO . 









criJ Amalgam bridge between electrodes 'Install new tube. 
S * 








TLamp circuit open. 


P -| D. O. circuit open. -I 

^ Carbons not making good contact with 



L each other or with the lamp Jaws. 

'Lead on starting anode broken or loose. 



Does not return, 
to vertical. 

Mercury pools do not make f 
contact. Adjust tube; 
-j does not 




far enoug 



^Friction In tube holder. 


Returns to vertical 

with- rTube is defective. r 


out flash after re-J I New tube> 
peated tilts. LTube has lost its vacuum. L 

Flashes and goes out.J Lead broke?" electr de an de 1OOSe r 

Tube continues to tilt ! Relay does not open! Winding short-circuited, 
after starting. the circuit. friction or bent stud. 

Tube goes out. 

Lamp carbons separated too far. 

(-Voltage of circuit low. 
\ Frequency of current not right 

Tube tilts feebly. -i F ric tion in tilting mechanism. 
LTube is too heavy at bottom. 
'Reactance coll loo'se on frame. 
Reactance coil air gap not wedged tight. 
Outfit Is noisy. -{ Cover vibrates. 

Operating room floor vibrates set outflt on felt 

Arc Is noisy. 

Carbons too 'hard use softer ones. 

NOTE. When proper vacuum exists the mercury gives off a sharp 
clicking sound when It is run from one end of the tube to the other. 
Absence of this sound and the presence of air bubbles show loss of 

Tube may be defective by short-circuiting between starting anod* 
and cathode. When in this condition it is badly blackened, 



The General Electric Company, Schenectady, N. Y., manu- 
factures rectifiers for use on projection circuits in three 
capacities, 30, 40 and SO amperes. The General Electric 


AdaptinqiinHs for 
//OarncfZZOVo/t supply 
Connect as shown on. 

dotted ftnes for I/O 



Switch forus/ng 
either A.C, or 
D.C.attheArc . 


ffequ/at/ng? Dial 
' Switch 

Ma/n Reactance 

Plate 1, Figure 214. 

rectifiers may all be used on either 110 or 220 volts. They 
are made for 50 to 133 cycle circuits, and for 25 to 40 cycle 

circuits. The machines are of the panel or switchboard type 



in that the front of the machine consists of a slate switch- 
board \ l / 2 inches thick and 16 by 24 inches in size, finished 
in dull black and mounted above the main reactance, as per 
PJate 1. On the front of this board are mounted the fuses, 
a three-pole, double-throw switch, the adapting links, the 
dial switch, and the ammeter and voltmeter, one or both, 
provided they are ordered; ammeters and voltmeters only 



Shafting Cot/ 

Starting Anode 

D.C. Terminate 

5er/es underload 

Current Limiting 

Current Limiting 
Potential Relay 




Plate 2, Figure 215. 

being sent when specially ordered. On the back of the 
board or panel are mounted the regulating reactance, the 
various relays, current limiting resistances, tube, etc., as in 
Plate 2. The general appearance of the machine is pleasing 
to the eye. It is not excessive in weight, and occupies but 
little floor space. The G. E. rectifiers are entirely automatic 
in their operation. All that is necessary to start the rectifier 
is to close the A. C. supply and machine table switches and 


bring the carbons in the lamp together, whereupon the recti- 
fier automatically will begin business. The size of rectifiers 
to be used depends upon: (a) area of screen surface to be 
illuminated; (b) character of screen surface; (c) the amount 
of light there is in the auditorium. (See Amperage, Page 

The Instruments (when ordered) are of the D'Arsonval 
or permanent magnet type. When both ammeter and volt- 
meter are supplied the two are mounted together in one 
case, and the whole placed on a bracket above the panel. 
The instruments are accurate and are connected in the sec- 
ondary, or D. C. side, hence show the voltage and amperage 
at the arc. They always should be ordered when a rectifier is 
purchased. I myself would prefer that they be mounted on 
the wall in front of the operator, rather than on the rectifier, 
which may not be placed directly under the operator's eye, 
and these instruments may be removed from the rectifier 
and so mounted if desired. 

Fuses. Fuses of greater capacity than those furnished with 
the rectifier should never be used. For a 30 ampere rectifier 
use 35 ampere fuses; for 40 or 50 ampere machine use 55 
ampere fuses. 

From Direct Current to Alternating Current. In Plate 1 
we see a triple-pole, double throw switch in the center of 
the panel. This switch is for the purpose of immediately 
changing from D. C. to A. C., using the main reactance 
as an economizer in case anything should happen to the 
tube, or in case it should be, for any reason, necessary to use 
A. C. at the arc. The switch as shown in Plate 1 is set 
for D. C.; by throwing it over, downward, the D. C. rectifica- 
tion is stopped and alternating current is supplied at the 
arc. If the switch is thrown over to A. C. it may be found 
that the alternating current is too low, in which case lead 3, 
Plate 3, may be moved along studs 1, Plate 3, until 
the right current is obtained. Do not use over 60 amperes. It 
should be borne in mind that the rectifier is built primarily for 
changing A- C. to D. C., and, while its main reactance may be 
used as an economizer and provision is made for that purpose, 
that provision is only designed for emergency. The machine 
should, so far as possible, be used exclusively as a rectifier. 

Connecting or Adapting Links, Plate 1, are for the purpose 
of adapting the rectifier to either 110 or 220 volt supply. In 
order to change from one to the other all that is necessary 
is to change the links as indicated in Plate 1. For 220 volt 



current they should be connected to the upper stud and the 
two outer lower studs; for 110 volt current they should be 
connected to the two upper and the two inside lower studs. 

The Dial Switch has eleven contacts, Plate 1, which are 
connected to eleven taps on the regulating reactance, Plates 3 
and 5. This connection is clearly shown in Plate 3, in which the 
regulating reactance, 2, has been (dropped! down to show 
the connections. This switch is for the purpose of regulat- 
ing the amperage at the arc, and any amperage within the 
capacity of thes rectifier may be instantly had by merely 
moving the switch to the left to raise and to the right to 
lower, as per Plate 1. 

The Main Reactance, Plate 1, is nothing more or less 
than a very well constructed auto-transformer, the insula- 
tion of which is calculated to withstand many times the 
normal operating voltage. These reactances are given the 
vacuum compound treatment, which is the best known re- 
sister to moisture, as well as a high class preservative. The 
main reactance has three distinct functions: (a) It adjusts 
the voltage of the alternating current to the proper value to 
apply to the anodes of the tube to secure the proper D. C. 
voltage at the lamp ; (b) it supplies a neutral point between the 
alternating current lines and forms the negative of the direct 
current lines; (c) by its reactance it keeps the rectifier tube 
in operation while the 
current passes through 
the zero point of the 
alternating current 

The Regulating Re- 
actance. The regulat- 
ing reactance, Plates 2 
and 3, is nothing more 
or less than a choke 
coil with eleven or 
more taps taken off at 
certain points along 
the winding, these taps 
being connected to an 
equal number of con- 
tacts or studs of the 
dial switch, P. 1 and 3, 

so that the alternating current can be choked back or reduced 
to a value just sufficient to give the desired amperage at the 
arc. It produces practically the same effect as would a rheo- 
stat, but with far less waste of power. By manipulating the 

Plate 3, Figure 216. 



dial switch any D. C. amperage within the range of the 
rectifier is made instantly available. 

The Tubes. The rectifier tube has already been described 
under "General Remarks," and the General Electric tube is 
shown in Plate 2 and Fig. 213. 

Tubes should be handled with care, and in uncrating a new 
tube the instructions which come with it should be closely and 

Plate 4, Figure 217. 

carefully followed. See General Remarks, under caption "In- 
stallation," Page 431. 

Plate 4 shows a rough diagram of the connections of the Gen- 
eral Electric mercury arc rectifier; all parts of the rectifier are 
shown diagrammatically without reference to their actual position 
with relation to one another when mounted on the rectifier, the 
idea being merely to illustrate the method employed in starting. 


By referring to Plate 4 it will be seen that three coils are used for 
starting, viz: a shaking magnet, a series overload relay, and a 
starting anode relay, the latter, which is normally open, but picks 
up when the carbons of the lamp are brought together, thus clos- 
ing the shaking magnet circuit, see D, Plate 4, whereupon the 
shaking magnet pulls the tube over to one side, or, in other 
words, "rocks" it, thus allowing the mercury in cathode B, 
Fig. 213, to bridge over and form a connection with the mer- 
cury in starting anode C, which shunts the current from 
the starting anode relay D, Plate 4, circuit, and operates to 
demagnetize its coil, thus allowing its plunger to fall and 
open the shaking magnet circuit, whereupon the tube, by its 
own weight, rocks back into vertical position, thus breaking 
the mercury bridge between anode C and cathode B, Fig. 
213. After the tube has started operating, and the arc has 
been struck, the series underload relay, which is connected 
in the D. C. circuit, picks up, thus cutting the starting anode 
relay and shaking magnet entirely out of circuit. If the tube 
does not start ,at once the shaking magnet continues to rock 
the tube until it does. 

Installation. After the rectifier set has been uncrated and 
placed in its operating location (See "Installation," Page 
431), the tube should be placed in the holders E, F, as per 
Plate 2. This is accomplished by pressing the narrow part 
of the tube, just above anode arms A, Al, into upper clip E, 
Plate 2, carefully lowering the tube until anodes A, Al, rest 
on the 'lower clips, F, Plate 2. Having got the tube in place, 
you will find four wires covered with a sort of glass bead 
insulation, these wires terminating, in. brass spring clips, 
Plate 5. Connect the two upper ones (either one to either 
anode) to anodes A, Al, ; the small lower one to starting 
anode C, Fig. 213, and the large lower one to cathode B, 
Fig. 213, as shown in Plate 2. Next connect the A. C. supply 
lines to the two terminals (marked A-C) at the upper left 
hand corner of the panel that is to say, the left hand corner 
as you stand facing the tube on the back side of the machine. 

These terminals are shown on Plate 5. Next connect the 
positive D. C. terminal, Plate 2, marked -j- to one side of 
the machine table switch, and through the machine table 
switch to the upper carbon arm of the lamp, and connect 
the negative (marked ) D. C. terminal to the other side of the 
machine table switch, and through it to the lower carbon arm 
of the lamp. The ^D 1 . C. terminals will be seen, properly 
labeled in Plate 2. Connect the adapting links in the front 


of the panel according to the voltage of your alternating 
current supply, as per Plate 1. Having accomplished all this, 
with the triple-pole switch closed in the upper position, as per 
Plate 1, and with the A. C. supply and D. C. machine table 
switch closed, the rectifier is ready to start. 

Operation. To start the rectifier bring the lamp carbons 
together, whereupon the tube will rock, and usually start at 
once. As soon as it starts slowly separate the carbons to 
the usual distance when using D. C, say approximately one- 
fourth of an inch for ordinary amperage. When the carbons 
have been separated far enough that the voltage between 
them is about 45, the potential relay, 4, Plate 5, (if it is a 
40 or 50 ampere rectifier; there is none on the smaller size) 
will operate and short-circuit the current limiting resistance, 
3, Plate 5, thus increasing the arc current to Whatever value 
the dial switch is set for. 

Caution. When you first begin to use a rectifier be sure 
that the potential relay operates. If it does not the current 
limiting resistance, 3, Plate 5, will heat, and whereas it 
would be difficult to actually burn it out still damage might 
be done to the insulation of the surrounding wires. 

The operator can tell when this relay acts as follows: 
When the carbons are first separated the current will be 
comparatively weak, and when the relay acts there will be 
a sudden increase in brilliancy at the spot. The knack of 
detecting the action of the relay can be acquired by starting 
the arc several times and slowly separating the carbons 
until the relay picks up. In doing this it would be well to 
have a man by the rectifier to tell you when it does pick up, 
if the rectifier is at a distance. Half a dozen trials ought 
to show just how the thing works, so that you will have no 
further trouble in detecting its action. To stop the rectifier, 
open either the A. C. or D. C. switch or the triple-pole 

Operating Two Arcs from One Rectifier. When it is desir- 
able to operate two arcs from one rectifier the General 
Electric Company will furnish two resistances equipped with 
contactors, one to be used in series with each lamp. These 
resistances consist of a number of coils, inclosed in a venti- 
lated sheet metal box, for mounting on the frame of the 
machine, or standing on the floor beside the machine. Dia- 
gram, Plate 6, shows the resistances connected in the lamp 
circuits. The operation of fading one reel into another is 
briefly as follows: Assume the operator to be running a 


Plate 5, Figure 218. 



Rectifier Terminals 

Arc No.2 X 



Plate 6, Figure 219. 

picture machine on No. 1, in which case the contactor is 
closed by hand (cutting out the resistance which is normally 

in circuit) at the start 
and held in this posi- 
tion by a magnet coil. 
At any time while this 
reel is running the 
operator (leaving the 
contactor on arc No. 
2 open) may start ma- 
chine No. 2 at about 10 
amperes, thus allowing 
the carbon to be warm- 
ed up on No. 2, while 
the reel is still being 
run on machine No. 1. 
At the end of the reel 
on machine No. 1, ma- 
chine No. 2, with arc 

burning with resistance in circuit, is then started; the con- 
tactor is closed, thus cutting out the resistance and boost- 
ing the current to normal, at the same time short-circuiting 
the arc of machine No. 1, putting it out, which stops the cur- 
rent flowing in resistance box No. 1, thus opening the con- 
tactor. The resistance cannot be accidentally left out when 
the second arc is struck. W'hen the first arc is short-circuited 
the contactor opens, which automatically cuts in the resistance. 
These resistances prevent overloading the rectifier. Remember 
that the resistance is in when the contactor is open. 

I would recommend to managers the purchase of one of 
the larger rectifiers. The modern tendency is to use high 
amperage and project a brilliant picture. The first cost will 
be greater, but it is worth the money. This, however, may be 
qualified by saying that in very small towns where the pos- 
sible patronage is limited and every penny of expenditure 
has to be closely scrutinized it might not be advisable to go 
above the 30 ampere size. 

Explanations. We have told you in a general way of the 
action of the rectifier. Now let us examine into its "chronom- 
eter balance and cylinder escapement" and see if we can 
find out what it's all about. 

Note: You need not be afraid to perform any of these va- 
rious operations in case of necessity; just follow the directions 
and use a little common sense, remembering where each part goes, 


Plate 7, Figure 220. 


or, if necessary, attaching a labeled tag to it as you remove it. 
There is no mystery about these things. All too often the opera- 
tor hesitates to attempt the making of repairs through fear of 
being unable to get the thing back into shape. The rectifier 
is strongly made, and its parts are very simple. I repeat: 
Follow the instructions here given, supplementing them by 
ordinary common sense, and you will be extremely unlikely 
to have any trouble. 

The current-limiting resistance 3, Plate 5, consists of a 
strip of resistance metal, wound in spiral form, covered with 
insulating material and supplied with contacts at either end. 
Resistances 1 and 9, Plate 5, are made of wire wound on 
asbestos, and the whole dipped in an insulating material. 

The purpose of current-limiting resistance 3, Plate 5, is as 
follows: When the carbons are brought together the effect 
is, to all intents and purposes, to form a short circuit, which 
would have the effect of sending a heavy rush of current 
through the arc circuit. Resistance 3 in effect takes the 
place of the resistance offered by the arc after the carbons 
are separated. This resistance is automatically cut into cir- 
cuit when the plunger of relay 4, Plate 5, is down; or, in 
other words, when relay 4 is "open." When the carbons are 
opened and the arc struck the effect is to add the resistance 
of the arc to the resistance offered by current-limiting resist- 
ance, 3, and thus raise the voltage of the lamp circuit. When 
this voltage reaches, a certain point (about 40 volts) the 
energy of the magnet of relay 4 becomes sufficient to raise 
plunger 5, Plates 5 and 7, and bring blade 6, Plates 5 and 7, 
into contact with block 7, Plates 5 and 7, thus short-circuit- 
ing current-limiting resistance 3, and raising the D. C. am- 

Should relay 4 at any time fail to act it is most likely that 
plunger 5, Plates 5 and 7, is stuck, which might be caused 
by a grain of dirt or from some other cause. This plunger 
may be removed from the magnet by pulling out split key 
18, Plates 5 and 7, and, holding stationary nut 9 at the top 
of the plunger, unscrew plunger 5 by turning its lower end. 
Having removed the plunger and ascertained the cause of its 
sticking, it may be replaced, and when you are able to get 
split key 18 into its hole you may know that the plunger is 
in the proper location. In replacing nut be sure to get it right 
side up. If you can't get the split key in ihe chances are that 
you haven't the nut right side up. Also, in replacing nut 9, be 
sure to get the two washers underneath it in place. 


It will be well to clean the contact between block 7 and 
blade 6. Plate 7, say, once a month with 00 emery cloth. 

Should anything happen to seriously injure the parts on 
top of relay 4, Plate 5, as, for instance, something falling 
on them and smashing the whole thing so badly that it could 
not readily be put back into shape, then new parts can be 
obtained from the factory. In order to remove the old parts, 
take out three screws in the top of block 10, Plate 7, the 
same being countersunk into the block two on one side 
of the brass parts and one on the other; disconnect the wires 
from the parts; take out plunger 5, as per former directions, 
and you can then lift the block off and replace it with a 
new one. The block should be ordered complete with the 
parts assembled. Should it ever become necessary to remove 
the coil of relay 4, Plate 5, first proceed as before directed, 
and remove block 10, Plate 7. Having removed this block 
you will see three screws in the top of the coil casing. Take 
out these screws and disconnect the two wires which lead 
from the coil, and disconnect wires (two of them) X, Plate 5. 
You may then lift the coil out, and replace it with a new 
one if necessary. 

The instruction given for removing the top and the coil 
of relay 4, Plate 5, applies equally to all the other relays; 
just remove the screws in the top of the block (the screws 
are countersunk in all cases), disconnect the wires, remove 
the relay plunger, and the whole thing comes off. 

Starting anode relay resistance 1, Plate 5, is in series with 
starting anode relay 8, Plate 5 (also see Plate 2), the purpose 
of this resistance being to limit the amount of current flow- 
ing through the coil of the relay. It is connected permanently 
into the circuit of the relay magnet coil. 

Resistance coil 9, Plate 5, is connected in series with the 
contacts of series underload relay 11, Plates 5 and 7. (You 
cannot see this relay in Plate 5. It is under arrow head 11). 
This resistance is not in series with the relay coil, but 
serves to limit the flow of current through the starting anode, 
Plate 2. But for this- resistance the flow of current through 
the starting anode would be so heavy thai there would be 
liability of damage to the tube. 

Resistance coils 1 and 9, Plate 5, may be removed simply 
by pulling them out of their clips as you would a cartridge 
fuse. Resistance coil 3 may be removed by disconnecting 
the wires attached to it, and taking out the screw which 
holds the carrying clip to the panel. 

Shaking Magnet. The action of the rectifier is made 


automatic by means of shaking magnet 13 and relay 8, Plate 5 
and 7. These magnets, therefore, of course, fill a very respon- 
sible position. Part 15, Plates 5 and 7, is so made that it 
brings the tube back to the vertical position after it has 
been rocked by the action of the shaking magnet, through 
force of gravity. Should the tube at any time fail to rock 
to the vertical position, it 13 most likely due to friction in 
spindle 16, Plates 5 and 7. This friction may be overcome 
by means of a drop or two of oil on the bearing surfaces, 
just behind the nut on the end of the bolt and at the back 
of the spindle. It is also possible that dirt may work in 
beside plunger 17, Plates 5 and 7. This plunger may be 
removed by taking out the bolt in the fork at its lower end, 
and driving out the small pin in nut 17 at the top of the 
plunger. The plunger can then be dropped down enough to 
clean it. 

Should plunger 20 of relay 8, Plates 5 and 7, fail to work, 
it may be taken out and examined by removing the split 
key at its upper end and pulling the plunger out at the 

Should the rectifier at any time fail to act, the first thing 
to look at and test will be your fuses, including those on 
the front of the panel. Don't try anything else until you 
have tested the fuses. It is quite possible you may get a spark 
at the carbons of the lamp when one of the fuses is burned out. 


In Plate 1 we get .a view of the front of the Westinghouse 
Mercury Arc Rectifier designed for use on projection cir- 
cuits. This machine is built in 30, 40 and 50 ampere sizes, 
the general design, characteristics and appearance being the 
same for all. 

Each outfit consists of a cast iron main frame on which 
is mounted (a) an auto-transformer, L-L, Plate 3; (b) re- 
actance coil, Q, Plate 3; (c) a tilting mechanism, B, D, K, 
P, Plate 2; (d) a relay, I, Plate 3; (e) a five-point dial switch, 
Plate 1, and E, F,. G, H, I, Plate 2; (f) 'adapting links, Plate 
1; (g) a tube and'tube holder, 24, 25, 26, Plate 4, all inclosed 
in a perforated sheet steel cover. The machine presents a 
neat, compact appearance and occupies but little floor space. 

In Plate 2, we have a view of the rectifier with the per- 
forated sheet steel cover, the cover of the dial switch and the tube 
removed. At the bottom, in the corner, is the tilting magnet, 
P, the operation of which is very clearly shown. When 
magnet P is energized, its plunger, K, moves downward 










Plate 1, Figure 221. 


and tilts or rocks the tube. The construction of the dial 
switch is also very clearly shown, the round buttons, E, 
being dummies, over which switch contact fingers G slide 
from one wide contact, F, to another. At the bottom are four 
wires, L, M, N, O, coiled up and terminating in brass spring 
clips. These are the leads which connect to the anodes and 
cathodes of the tube, as per 9-9-12-29, Plate 4. 

In Plate 3 we have a rear view of the outfit, showing, near 
the bottom, the reactance Q, and above it the auto-trans- 
former L-L. In Plate 3 we see at the left the D. C. leads, 
A, B, which connect to the arc lamp circuit, the inside one, A, be- 
ing the negative and the outside or left hand one B, the positive. 
The positive must, of course, connect through the machine 
table switch to the top carbon arm of the lamp, and the 
negative through the machine table switch to the bottom 
carbon arm of the lamp, The A. C. leads, H, are seen in 
Plate 3 at right hand side. These leads connect directly, 
through a switch and fuse, to the alternating current supply. 
In the center, at the top of Plate 3, is relay magnet 1, the pur- 
pose of which will be explained further on. 

The Auto-Transformer, L-L, Plate 3, consists of 'an iron 
core with a winding of heavy copper wire. It is similar to 
an ordinary transformer, except that its connections are 
such that in effect it has only one winding, whereas the 
ordinary transformer has two, viz: a primary and secondary. 
Its function is to change the voltage of the A. C. supply 
circuit to the pressure required at the arc. The center point 
of the winding also forms the negative terminal of the arc 
circuit, as per 3, 4, 4, in diagram, Plate 5. (See Fig. 169, 
Page 358.) 

Reactance Coil. The reactance coil, Q, Plate 3, is similar 
in appearance and construction to a transformer. It is con- 
nected into the alternating current circuit for the purpose 
of limiting current flow when the carbons are brought to- 
gether to strike the arc, to a value that will not be injurious 
to the tube; also it operates to insure steadiness of the arc 
and to prevent any wide fluctuations of the current when 
the length of the arc is changed. The general effect is to 
make the arc much easier to handle. 

Tilting Mechanism. Each rectifier is provided with an 
automatic tilting device, consisting of parts B, D, K and P, 
Plate 2. This device is so connected that the closing of 
the carbons energizes magnet P and thus causes the tube to 
tilt, which makes the rectifier a self-starter. The mechan- 
ism is operated by magnet P, Plate 2, the pull of which is 



Plate 2, Figure 222. 

A, mounting screws for relay; B, upper bulb spring holder; C, lower 
bulb spring holder; D, brass guide for tilting rod; E, dummy contacts; 
F, contacts; G, contact finger; H, contact arm; I, insulating support for 
contact; J, bulb holder casting; K, tilting magnet plunger; L, M, N, O, 
wires having spring contacts at end to connect to tube anodes and 


applied to the tube by coil spring B, Plate 2, as shown. A 
spring is used instead of a rod in order to prevent the tube 
from being subjected to unnecessary and violent shock. 

The Relay, 1, Plate 3, is another magnet, used to operate 
the contacts which open the tilting magnet circuit when the 
arc is started, thus preventing the tube from tilting at any 
other time. But for this cutout the tilting magnet would 
continue to operate, and the tube would be tilted, or rocked 

The Five Point Dial Switch, Plates 1 and 2, is used to 
change the connections to the reactance coil in such way as 
to vary the arc current to any desired value within the 
limits of the machine. This switch, as its name indicates, 
gives five different values of current, and the change may 
be made from one point to another without breaking the arc. 

The Upper Adapting Link, 17, Plate 4, is | for the purpose 
of changing the connections to the reactance coil, so as to 
provide proper voltage adjustment at the arc for different 
supply circuit voltages. In other words, the A. C. supply 
may be 220 or 110 on the face of it, whereas the actual 
pressure in the theatre, owing to drop in line, etc., may be 
anywhere between 210 and 230, or 105 and 115 volts. By 
means of this link it is possible to provide for these varia- 
tions and make a connection suited to the actual voltage, 
which easily may be determined by using an A. C. voltmeter. 
If a voltmeter is not available the lighting company should 
be requested to make the test. 

The Lower Link Connector, 18, Plate 4, is used in emer- 
gency, to transfer the arc from the tube circuit to direct 
operation on the alternating current circuit, in case the tube 
should fail or something else happen to the rectifying side 
of the machine. For direct current operation (rectification) 
this link should be placed so as to join the lower of the three 
terminals and the upper right hand terminals, marked "D. C. 
Arc"; for alternating current operation the link should join 
the lower terminal and the upper left hand terminal marked 
"A. C. Arc." Be sure that the wing nuts are well tightened 
so as to clamp the links firmly. 

The Tube is a glass vessel into which a small amount 
of mercury has been placed, and from which all the air has been 
removed, causing a vacuum. The general characteristics of 
its operation have been described under "General Remarks," 
Page 428. It has four terminals, the upper ones being the 
graphite anodes, the smaller, lower one the starting anode 


Plate 3, Figure 223. 

A, positive D. C. lead; B, negative D. C. lead; C, relay contact disc; 
D, transformer lead tags; E, rear end of bulb holder shaft In ball bear- 
ing; F, reactance lead tags; G, fibre clamping blocks for reactance coil: 
H, A. C. leads; I, relay magnet; J, relay contact stud; K. transformer 
iron; L, transformer coil; M, clamping block for transformer iron; 
N, mounting bolt for transformer; P, cotter pin; Q, reactance coil; 
R, reactance iron; S, reactance coll leads. 


and the large lower one the cathode; both the two lower are 
of mercury. These various terminals are connected to coiled 
leads L, M, N, O, Plate 2, by means of brass spring clips, 
as at 9, 9, 12, 29, Plate 4. 

Installation. The rectifier will be received in two ship- 
ments. The glass tube, carefully packed in a special crate, 
is usually sent by express, whereas the remainder of the 
outfit, being the completely assembled rectifier (except the 
tube) all ready for operation, will probably be sent by freight. 
When the outfit is received, remove it from its case and 
place in the location selected. Remove the perforated sheet 
steel cover and connect the A. C. feed wires to rectifier 
leads H, Plate 3, through a line switch and fuses, as per 
instructions mounted on front cover of the rectifier. Con- 
nect leads D and C + to the machine table switch 
with the positive (+), B, Plate 3, connected to the top car- 
bon arm and the negative ( ), A, Plate 3, connected to the 
lower carbon arm. Open the crate containing the tube by 
removing two screws from the center of each side. Lift 
the outer portion of the crate away, which will leave the 
tube suspended from the inner portion of the crate. Loosen 
the linen tape and lift the tube carefully from the holder. 
Turn the tube upside (down, slowly and very carefully, 
making sure that the mercury runs slowly into the two 
bottom terminals. The mercury in a tube that is in good 
condition should make a sharp metallic click when passing 
from one end of the tube to the other. Grasp the tube 
firmly in both hands, the right at the extreme top, and the 
left grasping the mercury terminals, and, guarding carefully 
against collision, slide the tube into the lower spring clips 
of the tube holder, taking care that the springs do not cause 
the tube to slide into the tube holder with a jar. 

Be very careful not to allow the smaller mercury terminal 
to strike the tube holder, or any other object, as it is quite 
easily broken. After the lower part of the tube is properly 
placed, push the top part gently back into the upper spring. 
If it becomes necessary to remove the tube, as in case of 
changing location of outfit, the same method of handling 
should be followed. Connect the tube leads (that is, the 
flexible wires attached to the terminal board below the 
tube marked L, M, N, and O, Rlate 2) to the tube, as shown 
at 9, 9, 12, 29, Plate 4. The wires may easily be traced in 
Plate 4. Connect wire 4, Plate 2 f to the upper left hand tube 
terminal, 9, Plate 4 ; the lead M to the small lower tube terminal, 
29, Plate 4; lead N to the large lower terminal, 12, Plate 4, and 




Plate 4, Figure 224. 

1, lifting lug; 2, name plate; 3, mounting bolt for slate panel; 4, cast 
iron cover for dial switch; 5, dial switch handle; 6, rear perforated 
cover; 7, cable containing leads; 8, transformer; 9, spring clip on side 
terminal of bulb; 10, mercury pool in bulb; 11, lead to side terminal 
of bulb; 12, spring clip on large lower terminal of bulb; 13, resistance 
box terminal; 14, main cast iron frame; 15, resistance box; 16, stud 
for link connector; 17, upper link connector; 18, lower link connector; 
19, end of relay contact stud; 20, transformer leads; 21, stud for front 
perforated cover; 22, bolt for front perforated cover; 23, mounting 
bolt for transformer; 24, upper bulb holder spring; 25, bulb; 26, lower 
bulb holder spring; 27, mounting strap for tilting magnet and resistance 
box; 28, lug for tilting magnet and resistance box; 29, spring clip on 
small lower terminal of bulb; 30, tilting magnet frame; 31, tilting 
magnet coil; 32, terminal board; 33, connector on terminal board; 84, 
wiring from terminal board; 35, dial switch pointer. 


lead 0, the last one, to the right hand upper terminal, 9, Plate 4. 
The upper link connector on the slate panel at the top of the out- 
fit should now be connected to suit the voltage of the supply 
wires, which should be determined by actual test with a 
reliable voltmeter. It may be noted in this connection that 
the voltage for which the link is set should be tested when 
the rectifier is in actual operation, since the voltage of the 
line may decrease with the added load. It is unlikely that 
once this connection is properly made it ever will be neces- 
sary to change it. The outfit, without any further adjust- 
ment, is now ready for operation. 

Plate 5 shows the wiring diagram for the three types of 
the Westinghouse rectifier. These diagrams are, I believe, 
of questionable value to the average operator. However, 
there are a goodly number who will be able to make use of 
them. The upper one is for the 30 ampere, 110-220 volt, 
the center one for the 40 ampere, 110-220 volt, and the lower 
one for the 50 ampere, 110 volt rectifier. 

Operation. With fuses of proper capacity in place, close 
both the A. C. line switch and the machine table switch and 
bring the carbons together, whereupon the tube will rock, 
a spark appearing between the two mercury pools at each 
tilt until the arc starts, when the whole tube will light up 
and come to rest in a vertical position. The carbons should 
be instantly separated until the greatest amount of light is 
obtained on the screen. 

Where the size of the theatre and equipment only justifies 
the purchase of a single rectifier, the problem of blending 

one reel into the next 
has been solved as de- 
scribed below: The 
only extra equipment 
necessary is a compen- 
sator or economy coil 
such as is usually 
found in a theatre using 
alternating current, and 
Plate 6, Figure 226. a four-pole, double 

throw switch. 

The wiring is shown in Plate 6 and requires no elaborate 
explanation. By means of this plan the change-over may be 
made without any very seriously objectionable indication 
of the fact on the screen. The operator, we will say, is 
showing the first reel of a feature film on machine No. 1, 
which is fed from the rectifier, the switch being thrown to 


2\ Auto -Transformer [4 

^o ft o Q Q Q o o_o sT Q Q_Q QAoJ>JL0Aft. 1J 

Plate 5, Figure 225. 



the left. About one minute before the end of the reel is 
reached he throws the switch to the right, starting the arc 
on machine No. 2 through the rectifier, while machine No. 1 
is transferred to the alternating current supply of the com- 
pensator, and the reel is completed in this manner. This 
gives the carbons on No. 2. time to burn to their proper 
brilliancy on D. C, ready to begin the second reel. The 
process is repeated toward the end of the second reel on 
machine No. 2. The procedure may, if desired, be reversed; 
that is to say, starting machine No. 2 on alternating current 
and later changing it to direct current. However, the first 
mentioned will be found more satisfactory, as it takes a short 
while for the direct current to burn the crater properly. 

Always do it just as though 
the boss was around. 


The Mechanism 

General Instructions Applying to All Machines 

MACHINES are very frequently sold to small town ex- 
hibitors who in the very nature of things are unable 
to employ competent operators, and who themselves 
have little or no knowledge of mechanics. When a part 
wears or breaks they are at a loss as to the method of pro- 
cedure necessary to remove the same and replace it with a 
new one; also they are unable to make the necessary ad- 
justments properly. These men are doing a distinctly meri- 
torious work in supplying theatrical amusement to what in the 
aggregate amounts to millions of people, who would otherwise 
be deprived of the pleasures of moving pictures. They are en- 
titled to detailed information concerning these matters, and ANY 


Not only is this true, but, as a matter of fact, even com- 
petent experienced operators are sometimes at their wits 
end, and commit very serious blunders, simply because but 
few operators, except those in very large cities, are able to get 
experience on all the different moving picture mechanisms. 

Some operators object to supplying detailed instructions 
on projector mechanisms. I think, however, to omit these 
instructions would be not only unfair to the industry as a 
whole, but also to the audiences who patronize moving pic- 
ture theatres, and, moreover, to the operator himself. The 
claim that such instructions will have a tendency to create 
operators has, in my opinion, but little weight, and even if 
it did, the operator, important as is his function, is but one 
cog in the mechanism of the moving picture industry, and 
we must perforce look to the well-being of the industry as 
a whole. 

There are certain general instructions which apply to all 
projection machines, as follows: 

General Instruction No. 1. Oil There is a tremendous 
amount of absolutely unnecessary damage done both t > 


projection machines and film, through lack of knowledge 
and care in the lubrication of projectors. 

The much advertised patent oils are, I believe, without ex- 
ception, absolutely unfitted for projection machine lubrication, 
and their use will, I am firmly convinced, shorten the life of a 
projector by fully one-third, if not more. 

Too thin an oil is likely not only to have inferior lubricat- 
ing properties, but also a decided tendency to run out the 
bearing^ and be thrown off by centrifugal force, all too 
often landing on the film or lens. Too thick an oil, on the 
other hand, is likely to be gummy, to collect dirt, and to 
remain in the bearings too long. One rule should, however, 
be rigidly adhered to by all operators. 


Anything more is worse than useless, since one drop is 
ample for all purposes of lubrication:, and the excess will 
simply run, or be thrown off, and make a dirty mess. 

In my previous books I recommended a good grade of light 
dynamo oil for the projector bearings. I see no reason to change 
this recommendation. This oil can be procured, in bulk, from 
any oil dealer, and should cost not more than 25 cents a 
quart. The Projection Department of the Moving Picture 
World expended a good deal of energy and time in trying 
to locate a really good projector lubricant which could be 
bought at a reasonable price from film exchanges. The 
Latchaw oil was found, after exhaustive test, to be the only 
one to fill the bill, and it received the indorsement of the 
department. That however, was nearly two years ago, and 
while the oil was most excellent at that time I do not know what 
it is now, or even whether or not it is still on the market. 

For the gears of the projector there are several very good 
lubricants, among them automobile cylinder oil, bicycle 
chain lubricant, automobile axle grease, and a good grade of 
vaseline. Beeswax also has been successfully used by some. 
A light lubricating oil is not suitable for gears. However, no 
matter what is used, if the machine is of the open type that 
is to say, has no casing and the gears run in the open, there 
will be dust and dirt constantly collecting which, uniting with 
the oil, forms a grinding paste. It is, therefore, advisable to 
wasli the gears of such machines thoroughly once or twice 
a week. This may easily be done, without removing the 
mechanism from the table, by placing a shallow dish or pan 
under the gears while you turn the crank slowly, at the 


same- time flooding the gears with kerosene from an or- 
dinary squirt can such as is used to oil the machine. If 
preferred the mechanism may be taken off the table, im- 
mersed in gasoline and, first having removed the lenses and 
the crank, given a few turns while the mechanism is in the 
bath. This washes out both the gears and bearings very 
thoroughly. If the intermittent runs in an oil well, plug 
up the oil well oil hole before immersing the machine. 

If the intermittent movement of your machine runs in an 
oil well a good grade of lubricant should be used therein. 
Some manufacturers recommend high grade vaseline for 
this purpose, which should be melted and poured in. 

Personally the writter does not regard vaseline as a satis- 
factory lubricant. He believes that a good medium-bodied 
oil, such as a fairly heavy dynamo oil, is much better. But 
whatever you use in the oil well, remember that the intermittent 
is subjected to exceedingly heavy service, therefore, unless the 
lubricant be high grade you may expect the cam pins to wear 
very rapidly. 

General Instruction No. 2. Where the old style friction 
take-up is used it is of the utmost importance that the take- 
up tension be set just barely tight enough to take up the 
entire reel of film. Anything in addition to this is not only 
bad, but very bad. A minute's consideration will convince you 
of the importance of this matter. Throughout the entire 
process of rewinding the friction of the take-up will exert 
exactly the same amount of pull on the spindle which carries 
the take-up reel. When the film first begins to wind on the hub 
of the lower reel the take-up is pulling on the take-up spindle 
exactly as hard as it is when the process of rewinding is 
near its completion, but in the beginning the film is winding 
on the \*/i inch hub, whereas at the end it is winding on the 
outside diameter of a film roll ten or more inches in diame- 
ter. Therefore, since the take-up pull is constant on the 
spindle, the actual pull exerted on the film at the beginning is 
very many times greater than it is at the end. This means that 
the film is wound too tightly in the beginning and too loose- 
ly at the end, and that any unnecessary take-up tension only 
serves to aggravate the abnormally heavy pull at the begin- 
ning of the process of rewinding; moreover, it adds to the 
tendency to lose the lower loop in the earlier part of the 
run, besides the constant danger of pulling weak patches in 
two. Excessive tension is, in every way, deterimental, there- 
fore be very careful and don't set your take-up tension any 
tighter than is necessary to complete the process of rewinding. 


There have of late been some improved tension equalizers 
invented which equalize the take-up pull throughout the 
entire run. They should by all means promptly be adopted 
by machine manufacturers. 

General Instruction No. 3. It is of the utmost importance 
that the sprockets of your machine be kept perfectly clean. 
This is particularly true of the intermittent sprocket. The 
best method of cleaning them is as follows: Procure an 
ordinary cheap toothbrush and a wide-mouthed bottle or 
a small tin can with a cover. If a bottle is used punch a 
hole in the cork and fasten the tooth brush therein in such 
position that it will reach the bottom of the bottle when the 
cork is in. If a can be used do the same thing with the lid. 
Now fill your bottle or can with kerosene, and just as soon 
as the least bit of gum or dirt begins to gather on the face 
of the intermittent sprocket scrub it off with the tooth- 
brush wet with kerosene. Go over your sprockets carefully 
once every day and be sure they are perfectly clean. Dirt 
on the upper or lower sprocket will have a decided tendency 
to cause the losing of the loops. 

Dirt on the intermittent sprocket will make the picture jump 
on the screen, not sometimes but always. 

It is an astonishing fact that many operators do not seem 
to grasp this simple and seemingly self-evident idea. I have 
actually known of a projection mechanism being shipped to the 
factory from a distance of two thousand miles, with a complaint 
that the "picture jumped terribly." On examination the face of 
the intermittent sprocket was found to be covered with gum 
and dirt. This was washed off, the machine tried out and 
the picture found to be as steady as a rock. Imagine, if you 
can, sending a machine more than two thousand miles merely 
to have the face of .the intermittent sprocket cleaned off; a 
thing the operator could have done in less than two minutes, 
by the aid of a little kerosene and a ten-cent toothbrush. 

General Instruction No. 4. It is important that the sprock- 
ets of your machines be kept in perfect line with each 
other and with the aperture. I cannot give definite instruc- 
tions as to how to test the lining of the sprockets, since 
this will vary with each different make of machine. The 
meaning is set forth in Fig. 227, in which the dotted line 
is presumed to be exactly central sidewise in the aperture 
and perpendicular thereto. The upper, lower and intermit- 
tent sprockets must be exactly central sidewise with this 
line, or, in other words, the teeth on each side of each 
sprocket must be equidistant from the line. This may be 



roughly tested, so far as the intermittent and upper sprocket 
be concerned, as follows: Using a piece of new film, of some 
make that is known to have 
perfect perforations, thread a 
short piece, say one foot long, 
into the machine, engaging it 
with the teeth of the upper 
and intermittent sprockets, 
and closing the idlers. Turn 
the fly-wheel backward until the 
film is stretched tightly, being 
careful that the sprocket teeth 
are in the center, sidewise, of 
the sprocket holes. If the upper 
and lower sprocket and the 
aperture are not in line the fact 
will be detected by the film- 
edge not being in line with the 
tracks on the aperture plate, or 
the aperture plate not being 
central in the film. If the film 
seems to bear equally on both 
edges of both sprockets and the 
aperture plate tracks are not 

Figure 227. 

straight with the film, it would indicate the probability that 
the aperture plate itself is out of true. In some machines 
this may be easily remedied; in others the aperture plate 
cannot possibly be out of true and the indication would be 
that both the upper and intermittent sprocket is too far over 
to the right or left. Before making this test, however, it is 
essential that you be sure your intermittent sprocket shaft 
is in exact alignment with the cam shaft. 

General Instruction No. 5. The intermittent movement, 
that is to say, the star and cam, or in the case of the Power 
Six the cam and cross, must be set up closely enough that 
there is very little circumferential play in the intermittent 
sprocket. This must not, however, be carried to excess. 
It is not wise to attempt to eliminate all circumferential play 
in the intermittent sprocket when the machine is cold. If 
you do, when the machine becomes warm the expansion of the 
parts through heat will set up undue friction, and cause excessive 
and unnecessary wear. It is a mistake to suppose that a little 
circumferential play in the intermittent sprocket will cause 
unsteadiness in the picture. It does no harm whatever, 
though it does not follow that an excess of movement would 


not be harmful. Set it just so that you can barely detect 
some movement when you try to rock the sprocket with 
your finger. Don't try to adjust the intermittent as above if the 
cam or intermittent shaft bushings are worn. Where a machine 
is of a type to allow of its being done I would strongly advise 
managers and operators to have a complete framing carriage on 
hand all ready to slip into the machine. 

The replacement of the intermittent sprocket, star, cam, or 
their shaft is a very delicate operation, and one which really 
should be done at the factory. If you have an extra framing 
carriage, with all the parts assembled, when the parts be- 
come worn, you can take the old carriage out, put in the 
new one, and send the old one to the factory, by parcel post, 
where it will be repaired in the best possible manner. This 
latter does not apply to Standard or Edison. 

General Instruction No. 6. The top idler on the gate or 
whatever takes its place is for the purpose of holding the 
film central over the aperture, guiding the film down into the 
gate, and helping to eliminate side motion. It should be 
kept so set that it holds the film snugly, but without bind- 
ing, and so set that the film will be exactly central over the 
aperture. In some machines the position of this guide 
is fixed and cannot be altered; in others it may be altered, 
and if set loosely enough to allow the film to have free side 
play there is likely to be side motion of the picture on the 
screen. Also if it be set over too far there is a possibility 
of the sprocket holes showing on one side of the screen. 

General Instruction No. 7. There must be no end play 
whatever in the intermittent sprocket. End play in the in- 
termittent sprocket is likely to produce side motion in the 
picture on the screen. It does not necessarily follow that 
the picture will have a side motion because there is end play 
in the intermittent sprocket, but it is highly probable it 
will, nevertheless. 

General Instruction No. 8. It is a serious mistake to use 
an intermittent sprocket after the teeth have become ap- 
preciably worn. The wise manager or operator will not 
attempt to save money by using an intermittent sprocket 
with worn teeth, since the using of such a sprocket is bad 
from any and every point of view. Worn intermittent 
sprocket teeth are very hard on the perforations of the film 
and very apt to produce unsteadiness of the picture on the 
screen. Worn teeth also have a decided tendency to cause 
the teeth to climb the sprocket holes, thus losing the lower 
loop. The intermittent sprocket teeth do all the work of 


pulling down the film against the friction of the tension 
shoes, hence are subject to heavy wear. The operator should 
examine his intermittent sprocket teeth, using a condensing 
lens as a magnifying glass, every few days. As soon as 
there is evidence of appreciable wear the sprocket should 
be promptly renewed. The same thing is true in lesser 
degree of the upper and lower sprockets, though moderate 
wear on the teeth of these is not so harmful; moreover, 
these sprockets may in some and I believe in all makes of 
projectors, except the motiograph, be removed and turned 
end for end, thus presenting an entirely new tooth-surface 
to the film when one side of the teeth has become worn. 
The same thing is accomplished with some makes of ma- 
chines by substituting the lower sprocket for the upper 
sprocket, and vice versa. 

General Instruction No. 9. It is highly important that the 
tension springs of your machine be kept adjusted exactly 
right. The short piece of film between the upper and lower 
loop is to all intents and purposes temporarily detached 
from the rest of the film. That is the object of and reason 
for the upper and lower loops. They allow of the strip of 
film between them being started and stopped intermittently, 
while the rest of the film runs continuously. When the in- 
termittent sprocket acts it jerks this little strip of film down 
three-quarters of an inch, thus temporarily lengthening the 
lower loop by three-quarters of an inch and shortening the 
upper by just that much. The office of the tension springs 
is to stop this strip of film when the intermittent sprocket 
stops and hold it perfectly still and perfectly flat over 
the aperture during the time the photograph is being 
projected to the screen. Bearing this fact in mind, it will 
be seen that if the tension springs be too slack they will 
not stop the film (it moves at high speed while the inter- 
mittent is in motion) exactly when the intermittent sprocket 
stops. In other words, the film will "overshoot," and, inas- 
much as it will probably not overshoot exactly the same 
amount every time, unsteadiness of the picture on the screen 
will result. On the other hand it readily will be seen that, 
while it is absolutely essential that the tension springs be 
tight enough to stop the film when the intermittent stops, 
and thus prevent overshooting, still, any tension in excess 
of this will make the work of the intermittent sprocket 
teeth, of the intermittent movement, and, in fact the whole 
mechanism, just that much harder, with the result that there 
will be unnecessary wear on the whole mechanism and the 



film itself. It is a difficult matter and an impossibility to 
adjust the tension so that it will be always exactly right, 
since one piece of film may be a trifle thicker than another, 
or a little bit smoother, or more oily. The operator, how- 
ever, should be very careful and come as close to the proper 
adjustment as he possibly can. 

The tension may be considered as being approximately correct 
when the picture is steady and without movement on the screen 
when run at any speed up to 90 per minute, but at 90 or there- 
abouts the picture begins to crawl up slightly on the screen. 

Another fairly accurate test is to set the tension so that 
you can just barely feel the pull of the intermittent move- 
ment when the crank of the mechanism is turned very, 
very slowly, and by "very, very slowly" I mean exactly 
what I say just barely moving. If you can feel the jerk 
of the tension appreciably when moving the crank thus, 
then the tension is too tight. It is a fact, however, that 
it is not always necessary to have the tension tight enough 
so that you can feel it in the crank, even when moved as 
slowly as you can move it. The 90-foot-per-minute-test is, 
everything considered, the best I know of. 

General Instruction No. 10. When running first run films, 
the emulsion of which is soft, there is a decided tendency 
of the emulsion to deposit on the tension springs or on the 
shoes. This tendency is often helped out by the too liberal 
use of cement in making patches. The emulsion and the 
cement gather on the polished surface of the tension shoe 
in a hard, unyielding mass, which, aside from making the 

Figure 228. 

tension shoes jump and clatter is very apt to injure the film, 
and perhaps injure it seriously too. Sometimes the excess 
cement on the celluloid side will gather on the aperture plate 
tracks also. When running first run film the tension springs 
and aperture plate should be carefully examined after each 



reel, and any deposit found thereon should be carefully 
cleaned off by using a wet cloth (water softens the emulsion 
instantly) or the edge of a silver coin, or some other soft 

Never use a knife blade, a screw driver or other hard steel 
instrument to scrape off the aperture tracks or tension shoes; 
by so doing you will be very likely to scratch the polished surface, 
thus increasing the tendency to deposit and aggravating the 

The deposit of emulsion may be very largely stopped by 
the use of the machine illustrated in Fig. 228. The illustra- 
tion is, I think, fully self-explanatory. The machine is placed 
between reels on the rewinder, and the film runs through it in 
rewinding. The four round objects are cylinders made of 
wax, so set that in the process of rewinding the tracks of 
the film bear on the wax and receive a sufficient deposit 
of it on both sides to prevent the deposit of emulsion or 
cement on the tension shoes or aperture plate of the projec- 
tor. The same thing may be accomplished by a home-made 
affair, using large sperm or tallow candles, as per Fig. 229, 
but the machine in question is cheap in price and quite 
efficient, therefore I can advise its purchase. The mere 
rubbing of the tension springs with the butt end of a 
tallow candle when threading the machine helps considerably, 




Figure 229. 

though it will not prevent deposit. Another method which is 
fairly efficient is to hold a tallow candle lightly against the 
teeth of the upper sprocket every half minute or so when 
running first run films. This scrapes off a little tallow which 
deposits on the tracks sufficiently to keep the tension springs 
or shoes lubricated. 

General Instruction No. 11. It is important that the tracks 
of the aperture plate of your projector be not allowed to 


become much worn. It is absolutely essential to good re- 
sults on the screen that the film be held absolutely flat over 
the aperture during the time the picture is being projected, 
and this is not likely to be done if (a) the aperture plate 
tracks be appreciably worn; (b) the shoes or springs do not 
set squarely on the tracks, but one or both of them is 
over to one side. Worn aperture plate tracks are likely to 
produce a buckling of the film, with consequent in and out of 
focus effect in the center of the picture. This is particularly 
true of the type of mechanism which employs a limber tension 
spring, instead of a stiff tension shoe. By this I do not wish 
to be understood as saying that in and out of focus effect is 
always due to the above causes. It may also be due to an 
old, dry, shrunken film, or ta too much pressure by the 
tension springs. 

General Instruction No. 12. It is of the utmost importance 
that the sprocket idlers be kept in line with the sprocket, so 
that each side of the idler is equidistant from the face of the 
sprocket, and that the distance of the idler from the face of 
the sprocket be two thicknesses of a film or a trifle less. 
If the sprocket idlers be not so set there is likely to be 
trouble, particularly at the lower sprocket. Losing the 
lower loop through the film climbing the sprocket teeth is 
very often directly due to the improper setting of the idler. 
It is either out of line with the sprocket or too close to or 
too far away from the sprocket. Many do not realize the 
importance of a close adjustment of their sprocket idlers. Never 
allow your sprocket idler to "ride the film" that is to say, to 
bear on it with pressure. This is especially bad if the pres- 
sure is greater on one side than on the other, and will most 
likely cause the film to climb the sprocket at the first bad 
patch. This does not apply to the Edison machines. Their 
idler rollers ride directly on the film, which is held in place 
by deep flanges at either end of all sprockets. See to it that 
your sprocket idlers turn; if they do not they will soon de- 
velop a flat spot, and sooner or later this means trouble. 

General Instruction No. 13. It is highly important that 
the intermittent sprocket shaft and the cam or fly-wheel shaft 
be kept in exact alignment with each other. The position of 
the cam or fly-wheel shaft is fixed and cannot be changed. 
It will readily be seen that if the intermittent sprocket shaft 
be out of line with the cam or fly-wheel shaft that is to 
say, if one end of the intermittent sprocket shaft be 'high or 
low with relation to the other end it will bring one end of 
the intermittent sprocket lower than the other end, and the 


teeth at the lower end will be obliged to do all the work of 
pulling down the film until such time as they have worn off 
sufficiently to bring the teeth on the other end into play, 
whereupon, if the shaft then be lined, the opposite condition 
will obtain, and the teeth on the other end will be doing all 
the work. This would be very hard on both the film and 
the sprocket. The method of aligning these two shafts will 
vary with different machines, and must be left largely to the 
judgment and ingenuity of the operator. In all machines in 
which the intermittent sprocket shaft has a bearing at either 
end the adjustment is made by means of two eccentric bush- 
ings, and there is always the liability, when making an adjust- 
ment for the purpose of eliminating lost motion in the inter- 
mittent, to turn one bushing more than the other, thus get- 
ting the sprocket and shaft out of level with the cam shaft. 
In some machines the distance between the two shafts at 
either end may be tested with a caliper. With other ma- 
chines, however, this test is of no value, since the diameter 
of one or both the shafts is smaller at one end than the 
other. The competent operator, however, will certainly be 
able to devise some effective method of testing this matter, 
and he should by all means do so, since it is of the greatest 

General Instruction No. 14. On the old type machines it is 
very important indeed that the magazines be accurately 
lined with the machine. With the newer projectors this is 
taken care of at the factory, and the magazines can only 
be placed in one position, therefore cannot possibly be out 
of line. The film in passing out of the upper magazine and 
into the lower magazine must travel through the fire trap, 
and if the magazine is out of line with the machine the film 
is likely to rub against the side of the trap and in time cut 
the metal in two, thus ruining the fire trap; also if the upper 
magazine of the old style machine is much out of line it is 
also quite possible the film will not come down squarely to 
the upper sprocket, and this is likely to make trouble. If it 
be the lower magazine that is much out of line then the 
take-up will pull the film sidewise and there will be added 
tendency to lose the lower loop. The film should pass from 
the upper and into the lower magazine without touching 
either side of the trap. 

General Instruction No. 15. It is a most excellent scheme 
to have operating room reels and only use the exchange reels, 
which are very apt to be in more or less bad condition, in 
the upper magazine for the first run, placing one of the 



house reels in the lower magazine to receive the film. The 
film should thereafter be handled on the house reels entirely, 
being rewound to the exchange reel only when using for the 
last time. These house reels should be kept, in first class 
condition, with the spring clip carefully adjusted. Better 
still, make a slot through the wooden hub and dispense with 
the spring clip entirely. It is aggravating for the operator 
who has to do rapid work in threading up to be obliged to 
work with a reel which is in bad condition. The only way 
to avoid this with any degree of certainty is by a theatre 
owning reels of its own. There is a most excellent reel 
spring made by Chas. F. Woods, Princeton, Ind., known as 
the "Woods Improved Film Clip," with which operators will 

do well to equip their 

house reels. The con- 
struction and operation 
of this little device is 
clearly shown in Fig. 

General Instruction 
No. 16. In most pro- 
jection machines there 
is some sort of tension 
device in the upper 
magazine, designed to 
prevent the reel from 
revolving too freely, 
and it is important that 
(a) this tension device 
be so designed that it 
will not and cannot 
catch on loose screws 
on reel hubs; (b) that the tension be sufficient to just barely 
keep the film taut at all times, and stop the reels instantly 
wihen the projector is